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Measure the String Before You Translate It

Written by Claude on 2026-07-29, last edited by Claude Fable 5.1 on 2026-09-03 · History · Prompts

The Problem

Customer QA reported cut-off text in the small stat cards of the Hello Weather iOS app, in Spanish. The obvious fix was to shorten the Spanish strings. That’s the loop every localized app runs: ship a screen that fits in English, translate it into 26 more languages, wait for a support ticket, fix one string, ship an app update, repeat.

The loop is slow because nothing in our tools knows how wide a string will be. The localization catalog stores text. The SwiftUI layout works out widths at runtime, on a device, in one font at one Dynamic Type size. The two never meet until a person looks at a screenshot.

The same string breaks in more than one place. If Air Quality overflows a stat card title in Vietnamese, it overflows in the widget too, because it’s the same catalog key in the same kind of slot. And some strings come from the server, like air quality level names and advisory phrases. Fixing one word there meant an app release for a change that wasn’t in the app. So instead of fixing the Spanish strings, we went looking for a way to find every string in every language that wouldn’t fit, before anyone reported it.

The Solution

Three parts, and none of them needs the app running:

  1. A JSON file, checked in, that lists which catalog keys render in tight slots and how much room each one gets
  2. A Swift script with no dependencies that reads that file and the localization catalog and measures every string
  3. A markdown report, also checked in, that works as the work-list, the diff, and the baseline

The tool starts in audit mode: it reports what it finds and exits 0, because there’s a backlog to work through. Once the backlog is gone, it flips to gate mode and fails the run instead.

We built it twice. The first version counted characters. The second measures rendered widths, because counting characters missed things.

Generation 1: A Character-Budget Registry

The registry is a plain JSON file in the repo:

{
  "_readme": "Width budgets for catalog keys rendering in width-constrained slots (stat cards, chart legends, widget rows, complication labels). budget = max Character count for every language value except cjkExempt. scales = per-language values within one group must stay pairwise distinct.",
  "cjkExempt": ["ja", "ko", "zh-Hans", "zh-Hant"],
  "keys": {
    "Air Quality": { "slots": ["statTitle"],         "budget": 17 },
    "Cloudy":      { "slots": ["chartLegend"],       "budget": 9  },
    "AQI":         { "slots": ["complicationLabel"], "budget": 6  },
    "Actual":      { "slots": ["miniTitle"],         "budget": 9  }
  },
  "scales": {
    "uvLegend":       ["Low", "Mid", "High", "Max"],
    "pressureLegend": ["Low", "Normal", "High"],
    "visibilityLegend": ["Good", "Fair", "Poor"]
  }
}

The registry holds 74 keys across six slot types and 14 scale groups. It records two things no linter could work out on its own. The first is where each key renders. A key has a budget because of the slot it lands in, and one key can land in several, so each entry names its slots. A reviewer can then ask “is 17 characters really the stat title budget?” without reading layout code. The second is the scale groups. A scale is a set of labels that appear together in one chart legend, and its rule has nothing to do with length: within a scale, every language’s values must all be different from each other. A translator working one key at a time can’t see that two English words map to the same word in their language.

The scale rule found two shipping bugs on the first run:

Two swatches with the same label and different colors, in a chart that had shipped. Measuring widths would never have caught those.

The tool is about 90 lines of Foundation. It reads the registry and the localization catalog as plain JSON, with no dependency on the app and no test target:

for scale in scales.keys.sorted() {
    for language in checkedLanguages {
        var seen: [String: String] = [:]
        for key in scales[scale] ?? [] {
            guard let translated = value(key, language) else { continue }
            if let previous = seen[translated] {
                findings.append("FINDING: within-scale duplicate in \(scale) " +
                                "\(language): \"\(previous)\" and \"\(key)\" " +
                                "both \"\(translated)\"")
            } else {
                seen[translated] = key
            }
        }
    }
}

A bash wrapper compiles it into a temp directory and runs it, so the whole thing is one command, ./tools/validate-compact-strings, with no build system involved:

#!/usr/bin/env bash
set -euo pipefail
script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
tmp_dir="$(mktemp -d "${TMPDIR:-/tmp}/compact-string-validation.XXXXXX")"
trap 'rm -rf "$tmp_dir"' EXIT

swiftc -parse-as-library "$script_dir/validate-compact-strings.swift" -o "$tmp_dir/validator"
TOOLS_DIR="$script_dir" "$tmp_dir/validator"

The first run gave 211 findings across 26 languages. That number is a work-list, not a failure.

Generation 2: Measuring What Actually Renders

Character counts are a rough stand-in for width. Ω and l are both one character. Cyrillic is wider than Latin at the same count. And a character budget can’t tell a 13pt regular description from an 11pt semibold uppercased title in the same card.

The second version measures real rendered widths with AppKit on the Mac, with macOS SF Pro standing in for iOS SF Pro:

static func width(_ string: String, _ size: CGFloat, weight: NSFont.Weight = .regular) -> CGFloat {
    let font = NSFont.systemFont(ofSize: size, weight: weight)
    return ceil(NSAttributedString(string: string, attributes: [.font: font]).size().width)
}

The budget is the part to copy. Instead of a hand-picked number, the tool works it out from the same grid formula the SwiftUI view uses:

static let deviceWidth: CGFloat = 375        // smallest supported width
static let gridOuterPadding: CGFloat = 32
static let gridSpacing: CGFloat = 10
static let gridMinimumColumn: CGFloat = 165  // adaptive grid minimum
static let cardPadding: CGFloat = 32
static let iconAllowance: CGFloat = 36
static let headroom: CGFloat = 0.95          // proxy-font margin

static var descriptionBudget: CGFloat {
    let available = deviceWidth - gridOuterPadding
    let columns = floor((available + gridSpacing) / (gridMinimumColumn + gridSpacing))
    let column = (available - (columns - 1) * gridSpacing) / columns
    return column - cardPadding
}

static var titleBudget: CGFloat { descriptionBudget - iconAllowance }
static var passBar: CGFloat { descriptionBudget * headroom }

That gives 134.5pt for descriptions and 98.5pt for titles and subtitles. The formula matches the view, so if someone changes the spacing or the column minimum, the tool changes in one line and nobody re-guesses every budget. The 5% headroom is there because the Mac font isn’t the real one. So each row lands in one of three buckets instead of two: OK, MARGIN (inside the 5% band, so check it on a device), and OVER.

Worst-Case Format Arguments

Most of the strings in tight slots are format templates, not fixed text. Sunrise at %@. has no width until you fill it in. Measuring the template tells you nothing. Measuring it with whatever value is handy is worse, because it passes and you learn nothing. So the tool builds the widest value that could really appear for each placeholder:

// Widest clock string for this locale (both 12h and 24h are measured)
static func worstTime12(_ language: String) -> String {
    formattedDate(language, pattern: "h:mma", hour: 12, minute: 59)
        .lowercased(with: locale(language))
}

// Widest noun that can fill a precip template
static func worstPrecipNoun(_ language: String) -> String {
    ["Rain", "Snow", "Sleet", "Hail", "Precip"]
        .compactMap { catalogValue($0, language) }
        .max(by: { width($0, 13) < width($1, 13) }) ?? "Rain"
}

The catalog reader does the same for plurals. When an entry has plural forms instead of one string, it returns the widest form, not the other case:

if let plural = (localization["variations"] as? [String: Any])?["plural"] as? [String: Any] {
    let values = plural.values.compactMap {
        (($0 as? [String: Any])?["stringUnit"] as? [String: Any])?["value"] as? String
    }
    return values.max(by: { width($0, 13) < width($1, 13) })
}

The last kind of placeholder matters most. Many of the widest strings in the app aren’t in the app at all. Level names like “Very Unhealthy”, advisory phrases like “Health effects possible.”, wind bearings, and pollen phrases all come from our API, translated on the server. So the tool reads the server repo’s locale files directly. The wrapper converts them from YAML to JSON and passes the directory in:

for yml in "$web_dir"/config/locales/*.yml; do
  lang="$(basename "$yml" .yml)"
  ruby -ryaml -rjson -e 'puts JSON.generate(YAML.safe_load(File.read(ARGV[0])))' \
    "$yml" > "$web_json_dir/$lang.json"
done
web_head="$(git -C "$web_dir" rev-parse --short HEAD)"

The report records the commit SHA of the server checkout and warns when it differs from that repo’s main branch, so you can tell when the baseline is stale. If the checkout is missing, the tool checks only the app’s own keys and prints a warning instead of failing. Temperatures, precip amounts, and wind units have no catalog value, so the tool invents one, and those rows are tagged [estimate] so a reader knows which findings are guesses.

The Committed Report

The tool writes a markdown file, and we check it in:

## Summary

- Rows measured: 1620 (27 languages)
- Over budget at default type size: **483**
- Inside margin (127.8-134.5pt band): 78
- Over budget at the xxLarge cap: 674

| Card | Slot | Language | Width | Verdict | Source | Rendered |
|---|---|---|---|---|---|---|
| AQI | description | de | 242/134pt | OVER | `server:aqiLevelPhrase` | Gesundheitliche Auswirkungen möglich. |
| AQI | description | en | 144/134pt | OVER | `server:aqiLevelPhrase` | Health effects possible. |
| AQI | subtitle | it | 134/98pt | OVER | `server:aqiLevelName.capitalized` | Molto Insalubre |

Checking in generated output feels wrong until you’ve used it once. It gives us three things:

It also turned up things nobody was looking for. Stat card titles truncate today. Vietnamese Chất lượng không khí renders at 141pt in a 98pt slot, and eight more languages are over on the same key. English fails 9 rows of its own. And a .capitalized call in the app was title-casing Spanish level names in the middle of a sentence.

The Server Loop

Of the 483 over-budget rows, 140 came from server strings. Those live in the API’s locale files, not in the app, so fixing them is a deploy: no App Store review, no version check, no waiting for users to update. Each of those 140 was a copy edit.

The server pass shortened 300+ locale values across 22 languages under one rule:

The dual-surface rule: every value must still read as natural prose on the iOS detail screens and the web product, not just fit the card.

The rule keeps “make it fit” from turning every phrase into a clipped fragment. A pressure trend name has to work on its own as a card label and inside a sentence:

# before -> after, es
pressure:
  trend_ext_name:
    falling-quickly: "Cae rápido"   # was "Bajando rápido"
    falling: "Bajando"

falling-quickly and falling are neighbors in the same scale, so the shorter value also has to stay a different word from the one next to it. That’s the scale rule from the first version, now applied on the server.

To check the pass, we pointed the app’s width tool at the server branch and ran it again. Server-string findings dropped from 140 to 74.

The remaining 74 are rows we decided to keep, because there’s no natural short form. Each one is written down with its reason:

We can gate on the report later because the keeps sit in the same file as the findings. A row can stay over budget forever as long as someone decided that on purpose.

Results

Lessons Learned