I deal with it that way that I put i18 package to ignore group so it won’t hold my general system updates. Then when update of ff-kde-opensuse comes I just install i18 package manually.
Lately ff-kde-opensuse is updated very quickly so this not a problem, at least at the moment.
I wish there were thunderbird-kde-opensuse version. In Thunderbird we deal with attachments very often so having kde-dialogs would help a lot. At the moment we can only use thunderbird-appmenu AUR package but this has to be compiles and compiling Thunderbird is a pain, it’s more problematic then FF (lasts longer and is easy to run into various problems so we have to re-launch many hours compilations many times… I wish there were bin version, I would took it, because compiling Thunderbird is so annoying).