New Score dialog: template categories and titles are displayed untranslated

Describe the bug
On the Templates page of the New Score dialog, the categories and titles of the templates are displayed untranslated.

Additional context
This will be a bit tricky to solve, since the names of the categories come from a json file (share/templates/categories.json) and the titles come directly from the content of the mscx files, so both are not in the code. That means that they can't be extracted to make them translatable.

So, either we need to extract them automatically into a (fake) code file, or do it manually (so that we can extract the strings from that code file). Doing it automatically is difficult (involves reading mscx files), and doing it manually is cumbersome too (prone to human errors). So I'm not sure what to choose.

This problem has been known and re-forgotten a few times, so I thought let's open an issue for it so that we don't miss it again.