I know this one will sound stupid when first read, but please hear me out.

Number formatting.

Currently item stacks use String.valueOf to format the number of items. This assumes that the entire world wants to see these digits:

0123456789

But for example in some Arabic locales, though, the users want to see these digits:

٠١٢٣٤٥٦٧٨٩

Instead, I would like Minecraft to use NumberFormat.getIntegerInstance().format(value). The formatter can be cached for reuse and has fast-path rendering so I would even hope that performance not be a problem.

For message strings, if any happen to contain numbers I would hope that MessageFormat is already being used, and ideally ICU's as Java's doesn't deal with Arabic well either.