Increase threshold for including translations

With !185 (merged) I realized that 50% might be not enough for us to include languages for future releases. Ukrainian is only around 50%, and while a lot of important strings are already translated, there's still a lot of stuff missing.

I suggest aligning Desktop's policy with Android's one and set the threshold to 80% for future releases.

What to do with languages that are included but under 80% is open to discussion.