IMHO, you have a reasonable concern. If we are going to ask to test alpha versions of things, we ought to have some process to release nightly builds that work with unified installer?
Since we do not, I think it should be a fine shortcut to submit translation bugs, if:
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You see them in currently released Plone 5.0.6, and...
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You compare the .po files to master branches on github, to see if anyone actually tried addressing this in 5.1. That is easy enough in a browser:
a. Determine package the .po file in question lives in locally (in your eggs directory);
b. Go to https://github.com/plone/${PACKAGENAME} to browse source, and find the .po file on the same relative path as it exists inside the egg distribution for the same package.
Sean