Error message phrasing is really very important, but it’s probably better to have that refined in code review or to have some explicit step for it.

Error message phrasing should not be in code. It should be in localization files, even for the default language, and not require a developer to modify.

Depends on the requirements. I've had many internal-only applications only require one language: English. At that point you can hard code many things, which skips the loading other files, checking different languages, etc.

I'd still rather the exact wording isn't in code, personally:

    get_msg('fail_add_address')

vs.

    'I\'m sorry, we\'ve been unable to add the address %s at this time,' \
    ' please try again later.'

(... but that's an ideal I have without ever having worked with it, so what do I know, and ymmv, etc.)

And what is this localization file called? We do not have a system where non dev can commit any change in our product.

We do have a constants file which has all the messages but a PM does not access to code/commit and has to go via a Dev.

It really depends on who‘s the target group. I hate localization in Developer Tools etc, because googling it is harder and a lot of times English is just easier to understand. It’s different for a shopping site.

How would you know this without entering their personal space?