I've previously contributed an update for the German translation, and this response reflects on the experiences I had as a contributor. Dan will have the final decision on merging AFAIK.
I see that an Ukrainian translation existed before, and you are updating it.
TL;DR: go ahead and create a PR.
The longer version:
- create a fork (you've already done that)
- create a branch (good practice to not create a PR from the master)
- create a pull request with a helpful description
- the automatic continuous integration (travis & appveyor) will run all tests
- if a test fails due to a translation change, push some more change; maybe cleanup git history first and use force-push
- if all test succeed, wait for the PR to be merged
Cheers, Alexander