Previously only one translation file per locale could be loaded.
Now the user can specify multiple files per locale, and the translations
from each of these files will be merged together by message id.
The merging is on a first-wins approach. So if to you have three files
to be merged:
```
['a.xlf', 'b.xmb', 'c.json']
```
Then any message from `a.xlf` will be used rather than a message from `b.xmb`
or `c.json` and so on. In practice this means that you should put the files
in order of most important first, with "fallback" translations later.
PR Close#36792
72f534f7f8