As a native speaker, I am amazed that in Romanian the name of Wales, when it was introduced, very probably in the 19th century, was translated as Ţara Galilor, literally "Country of the Gauls", unlike in any other European country — where, instead, we find either
the English form "Wales" (Slavic and German languages, Hungarian, Baltic, Albanian), or
a Latinized version of the name similar to the French Galles (Pays de Galles, where Galles is not a plural, like in Romanian, but the transposition of the term Wales, I think; see this answer on how Wales/Welsh have evolved in English).
I have initially asked a related question on the history site which then was moved here: Excepting Romanian, was "Wales" ever translated in modern times outside English with the same term as that meaning "Gaul" or "Gauls"?.
The term Ţara Galilor is also odd in that it has a rather archaic form, without many precedents. It follows the old structure of the Romanian endonym of Wallachia, Ţara Romanească (literally "Romanian Country"), applied in the past to other countries, but which is not applied now to any modern name of a country or state, except Wales: it survives only in the archaic/poetic naming of old regions of Romania, especially from Transilvania, like Ţara Lăpuşului, Ţara Oaşului (for Lăpuş/Oaş regions), in the historical name of The Lower Countries (Ţările de jos) and in the name of the Tierra del Fuego (Ţara de Foc)
Repeating from my other post:
My scenario about what happened is that at a stage when the common knowledge on the Great Britain was somewhat fuzzy, Romanian journalists translated Pays de Galles as Ţara Galilor; at that time there was no word for Welsh in Romanian, but there was already one for Gaul, which had been constructed directly from Latin, in the form gal. But when the same type of people were looking for a Romanian translation for Wales/Welsh they could not use Latin and so used French, where the term for Welsh is gallois, while for Gaul it is gaulois; but they neglected the 1-letter difference and considered those terms as identical. As Gaul already existed in Romanian as gal, they simply transposed into Romanian the false identity between gallois and gaulois. This was not done because they were aware of or interested in the common origin of those two terms, but because their French was not perfect. The erroneous translation entered the common use and even dictionaries: but the only dictionary that I could find where "gal"/"gali", meaning Gaul/Gauls, is used for "modern inhabitants of Wales" (with an example for the Prince of Wales as "principele Galilor", that is "the Prince of the Gauls") dates from 1923. As far as I know, in later dictionaries the error was partially corrected: Welsh became galez/galezi - fem. galeză/galeze (similar to other Romance languages), but the name of the country still reflects the old mishap.
Other hypotheses can be imagined:
a cross-contamination from Greek and French into Romanian: in Greek, where the name of Gaul is Γαλατία, the name of Wales is Ουαλία, which might have seemed close to the Latin Gallia, and thus encourage a confusion between Welsh and Gauls.
an ignorant reader of the French terms "Prince de Galles" or "Pays de Galles" who barely understood French but knew the recent Romanian word gal for Gaul, could have translated "de Galles" as "of the Gauls".
the influence of the (somewhat dubious) theory of "Popular Wallachias" (or "Romanias"): Romanian Wikipedia page here, in French here, while the English linked page doesn't follow the same content. The theory is a bit more complex, but basically it tries to name "Wallachia" (or more or less vaguely relate to that) any region which at some time or other was called with a term based on the German root
walazmeaning non-German, then Celtic, Roman, neo-Latin, Italian, Romanian. As on the odd map of those half-imaginary entities Wales is also mentioned (because its name is based on that same root), while Gaul is named Walha, and given that the form
Ţara...is also traditionally used for Romanian old regions, some of which are identified in this "theory" with one "Wallachia" or other, a such influence could have contributed to the creation or at least to the conservation of the form Ţara Galilor, as it encourages both the use of the old/odd form Ţara... and the identification between Wales and Gaul/"Walha".
- in the context of any of the above, the common origin of all the terms involved here - the old German root naming foreigners (the fact that Galles/Wales, Welsh, Gallois, Gaulois, Waloon, Wallachian, etc have the same root) could have acted as a facilitator, although obviously the common origin doesn't change their very different meaning.
My idea is that this error was made rather recently, sometime between 1830 and 1890. But I do not know exactly when.