Add binary MO translation file support.

[bruvzg]

Adds support for binary MO files (same features, but smaller).

TODO:

• Test context and plurals are loaded correctly (neither seems to be actively used by the engine)

Also, added an extra check for text PO loader, to prevent crash in case of invalid "Plural-Forms" string.

Node: with the currently enabled editor / class-ref translations, converting them to MO can decrease editor binary size by 1.6 MB (probably substantially more if incomplete translations are included).

[akien-mga]

Looks great!

I assume that to actually benefit from this in editor builds we'd need to add a buildsystem step using gettext to generate the MO files? (Probably optional, if gettext is found.)

[akien-mga]

Thanks!

[bruvzg]

I assume that to actually benefit from this in editor builds we'd need to add a buildsystem step using gettext to generate the MO files? (Probably optional, if gettext is found.)

Yes, we have to run msgfmt xx.po --no-hash -o xx.mo for each file, I have not added it since gettext is usually not available on Windows/MSVC setups, but I guess making it optional is also OK.

[Calinou]

Like #59275, I wonder if this could benefit from a 3.x backport (along with #59483). It might not be too difficult for me to do, I'm just asking here in case there's a blocker or you've already started a 3.x backport.

[bruvzg]

Both should be easy to backport, but 3.x editor use smaller number of fonts so impact would be less as well.

[bruvzg]

I have not fully tested it, but it seems to remove almost 7 MB, so probably worth it - #59522