Quick answer: Format money with a currency-aware formatter that takes both the amount's currency code and the display locale, so the symbol, placement, and grouping all come from the rules.
Showing $9,99 to a French euro player gets both the symbol and the separators wrong. Formatting with the currency code plus the display locale yields the right symbol, the right side, and the right separators.
How to fix it
1. Format by currency and locale
Use a currency formatter that takes a currency code (like EUR) and a display locale (like fr-FR), for example Intl.NumberFormat(locale, {style:'currency', currency}), so symbol and placement are correct.
2. Separate currency from language
Remember the price's currency is fixed by what you charge, but its presentation follows the player's locale; keep those two inputs distinct rather than tying the symbol to the language.
3. Avoid manual symbol prefixes
Never write "$" + amount; that hardcodes one currency and one position and breaks for every locale that places the symbol after the number or uses a different glyph.
Catching the ones you can't reproduce
The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.
Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.
This is where a tool like Bugnet earns its place. Its SDK captures every error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.
A crash you can name from its stack trace is a crash you can usually fix in minutes.