Merging .po-files with Git is painful.

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

There have been attempts Show archive.org snapshot of making Git more clever when trying to merge .po-files. I believe however that this is not enough as it can still produce invalid .pos (usually due to double definitions), which can seriously confuse gettext afterwards.

Lacking any more secure solution, I think you should avoid editing po files in different branches at the same time. In order to not accidentally produce invalid merges I additionally disable merging for po files altogether, by adding the following .gitattributes file to the root of the repository:

*.po   merge=binary
*.pot  merge=binary