Nor has anyone ever explained convincingly why the “continental” branch of West Germanic (the one that eventually became German in all its dialects, and Dutch and Friesian) dropped the al- word for “beer” it had derived from a supposed Germanic root *aluþ- (that *, remember, indicates a word for which there is no direct evidence, but which has been reconstructed from later forms), and took up the word bier instead, while the “off-shore” branch of West Germanic, the ancestor of modern English, together with the North Germanic languages (Norwegian, Swedish, Danish and so on) stayed with words derived from *aluþ- – “ale” in modern English, Swedish öl and Danish and Norwegian øl.
Let’s look at “ale” first, the word that originally, in English, mean an unhopped fermented malt drink. It’s a word found across Northern and Eastern Europe: as well as in the Scandinavian languages, it occurs in the Baltic languages Lithuanian (alùs) and Latvian (alus), the Finno-Ugric languages Finnish (olut) and Estonian (olu) and the Slav languages Slovene (ôl) and Serbo-Croat (olovina, which means “yeast, dregs”, I believe). There is no evidence that the Baltic languages borrowed the “ale” word from the Germanic languages, or vice versa.
The word also appears away over in the Caucasus, in Georgian (apart from Finnish and Estonian the only non-Indo-European example) as ludi or, in a couple of mountain dialects, aludi, and in Georgian’s neighbour, the Iranic language Ossetian, as aeluton. Georgian linguists believe their language took the word ludi from the Ossetians, who are the descendants of the Alans.
The Alans ranged from their original home near the Sea of Azov, north of the Black Sea, as far west as France in the late 4th, 5th and 6th century AD, down into Spain and along the North African cost to modern Tunisia, as allies of other invaders of the Roman world such as the Germanic-speaking Vandals and Goths. After the final defeat of the Vandal/Alan kingdom in North Africa in 534, some of the Alans look to have returned to the border of the Roman Empire with Persia as cavalry in the Roman army. It seems more than possible they picked up the “ale” word from one of the Germanic peoples and brought it back to the Eastern Black Sea, where they met up with other stay-at-home Alans who had been pushed up into the Caucasus by the advancing Huns.
But where does “ale” come from as a word? One school wants to trace it to an Indo-European base *alu- (-d, -t), meaning “bitter”, a root found in the modern English word “alum”, the highly astringent salt used in, for example, leather tanning, and in the Proto-Slavonic root *el-uku, “bitter”, which has apparently given words such as the dialectic Polish ilki, “bitter” and the Czech žluknouti, “turn rancid”. This would make ale etymologically “the bitter drink”. Unfortunately there’s no evidence ale WAS originally a bitter drink: without hops and herbs (and English ale, at least, seems to have been drunk quite often without herbs) it would probably have been a sweetish drink to begin with, and then acidic or sharp, rather than bitter, as it aged and soured. Indeed, in a list of words in one now-extinct Baltic language, Old Prussian, compiled by a German writer in the 14th century, alu is glossed as meaning “mead”, fermented honey, which is definitely sweet, not bitter. So, no cigar for that idea.