@Brecht Van Lommel (brecht) In general the only string that should use TIP_ are the tooltips that show up on mouse hover, right? Just want to be sure, then I can fix this stuff when I run into it.

@Hans Goudey (HooglyBoogly) indeed, that's how I would expect the option to work. The idea being that you can enable just tooltips and have interface completely in English, except when hovering over buttons.

Do you think it's fine to commit those fixes or would a patch be necessary?

You can commit those fixes directly.

While looking into this I actually found this commit from @Bastien Montagne (mont29): rB23df1a774b5b

I realized I was mostly reversing those changes so it's probably best to talk about it first.
There seems to be lots of confusion about what the "Interface" property in preferences means.
I get the argument that these strings are sort of like tooltips, but it doesn't seem clear to me that
that setting is meant to change reports and status text as well. That's why we get bug reports about it.

Admittedly I don't have the experience of using Blender in a language besides my native language, but
I would suggest a couple options:

1. Add a third option for for reports and messages
2. Clarify the meaning / name of the "Interface" property
3. Only translate these areas with interface translation turned on.

From what Hans linked and explained, there is a design question. And what's reported here is an intentional change. So changing this into a known issue, it's not a bug.