There's a lot of ways to do this, and I bet there's a way where modern Germany could be swamped with East Germanic peoples which leads to most or all of the modern German-speaking world (including Low German languages) speaking some East Germanic tongue, maybe a fusion of Burgundian, Gothic, Rugian, etc. These East Germanic peoples might leave groups back in modern Poland, some of whom might still speak their ancestral language, and of course if you have East Germanic groups in an area as big as the German-speaking part of Europe, you'd have a lot of linguistic variation. Like say the Burgundians settle in Alsace + Baden and the Rugians settle in Austria, you have two different East Germanic languages which will end up being significantly different from each other over time. But a language is a dialect with an army, so we might only have one "German language" even if we have a "Rugian language" and a "Burgundian language" which are significantly different (as much or more than Spanish and French) yet still are considered only dialects of each other. The problem is finding a way where West Germanic speakers are replaced or assimilated by East Germanic speakers.
But more plausibly, I think if the Gepids had been in the right place like the mountains of Transylvania, they could assimilate Romance speakers, Slavs, Magyars, Cumans, etc. and their language remain strong. At most, these Gepids could entirely replace Romania in history, leaving the Aromanians and such as the only representatives of Eastern Romance languages. And maybe you could have a second group along the Vistula or somewhere who maintain their identity as (Arian, but maybe later Catholic/Orthodox) Christians against the pagan Slavs. You might be able to have a few groups like this, maybe a bit like how there's many Eastern Romance-speaking groups (and historically a few more which assimilated in Early Modern times). I think Austria/Slovenia might be a good place for this, where we might have Rugians migrate into the mountains and maintain a separate culture from other German speakers. The Crimean Goths would play into this too, being able to maintain their language TTL instead of being assimilated into some other Germanic speaking (yet non-East Germanic) population which took their name like OTL.
To me the easiest PoDs are those that have the least dramatic effects. With that in mind I’d try to sketch out a scenario without massive Migration Era changes.
The 530 Vandalic coup in Carthage fails and relations between the Vandalic Kingdom and the Eastern Roman Empire remain cordial. Eventually, instead of outright conquest the Vandals become clients of East Rome; they experience a cultural golden age and manage to have the Bible translated into Vandalic.
The Arabs still expand during the 7th century and North Africa is overrun and conquered. However, members of the Vandalic court and leadership flee by ship to Malta, which they have been fortifying against Ostrogothic or Lombardic invasion for decades. Eventually, Malta speaks a highly divergent form of the Vandalic language.
Meanwhile, the Gothic tribes of Taurica find success under a less stressed Byzantine Empire in later centuries. Eventually, their language becomes the lingua franca of Byzantine territories in the region.
The Vandals were pretty assimilated into North African culture, though, and pretty quickly. Their leaders were supporting Latin-language poets, and Latin was still the dominant language as it had been for centuries. I can't imagine there'd be a lot of demand for a Vandal Bible when the majority of Vandals ended up speaking Latin before long. They were just a minor element on the cultural fusion between Roman, Berber, and Punic culture, even if they were the ruling class. I think you'd need a Vandal equivalent to the Ulfilas Bible which would need to be written around the same time.
Malta is definitely a plausible refuge point for the Vandalic language though, since OTL it could easily have been one for African Romance languages or Punic.