Translation:The girl does not eat this onion.
It is rather a different thing. The book mine, though, also exists in Norwegian as book-the mine, and as I pointed out, Swedish and Norwegian both have this book-the. That appending of the definite determiner on the back is something you see all over the Balkans, for instance in Albanian, Bulgarian, and (when we see it on Duolingo soon) Romanian. That possessive on the end in Greek looks to me like it is a genitive, but I suppose it might be this kind of an areal feature of appending these kinds of things on the end of the noun. I guess it might even be seen as being like Turkish, in which the possessive is an ending, as in Hungarian.
Well, actually, ID-07's second example is actually more like "man-the this is good," so it does have "this" directly after "the," they just come after the words they modify, unlike your second Spanish example. That's a really interesting construction in Spanish, though.
That's true, but the concept of the word in that sense may be somewhat artificial. Chinese has sets of words that are quite regularly used in the same sets, so we could think of them as being a longer, multisyllabic word (though I can't think of any as long as many German or Turkish words) instead of several monosyllabic words. What does it matter for instance, whether we write improvised explosive device or sexual ly transmitted disease as three words or one word? It is just an artifact of our writing conventions.
The fascinating thing to me is that you have that appending of the definite article in Romanian, Bulgarian, and (I believe) Albanian. I would not be surprised if whatever influenced them all to do that (since no other Romance or Slavic languages do that) might also have influence Modern Greek.
Regarding the use of suffixes/prefixes, in lieu of separate words, the concept is not that unique. It may be for the definite article but I assume you know that Hebrew had the generic concept of attaching prefixes for quite a few years now! And THEN there is German! I am sure the list goes on... I find Chinese interesting in the way it builds complex structures from simple ones.
The Hebrew article, like the Arabic, is indeed usually written without a space between it and the word, though I am not sure when word breaks developed in Hebrew. Definiteness in the noun is displayed in some languages with a suffix (Basque comes to mind), but that is relatively uncommon in Indo-European languages, except in the Balkans and Scandinavia. German, like Dutch, English, and Frisian, indicates definiteness with a separate article (der, die, das). Analytic languages, like Chinese, are interesting in that way. Duolingo, of course, has Vietnamese (which I am enjoying, but the betaness of it is so frustrating I had to take a bread). The distinction between an analytic language, like Chinese, and an agglutinative language, like Hungarian, though, may not really be so stark. To some extent it has to do with the writing system, which separates out Chinese grammatical markers as particles, while a similarly functioning syllable in Hungarian or Turkish would be considered an ending appended to the noun. This was actually pointed out to me by my sister, who has lived in Japan for decades now, and pointed out to me that my various Hungarian noun cases really functioned like her various Japanese particles.
I was talking more about 'gluing' of any 'words' together. For example, in Ancient Hebrew, the word 'and' (among others) is prefixed (as a letter) to the linked word. In German, words are glued to make VERY long words. In Chinese, multiple 'words' might be compacted into a very small picture. Whatever people call the terms, the concept is the same to me.
Semantically, I find the Spanish, Romanian and Greek to be in the same boat in this case. Why use the definite article 'the' if you already specified the object with the definite pronoun 'this'? Other languages have similar concepts where you need two words to make a negation (French for example) where most other Indo-European languages don't! In the case of Romanian, there is an explanation for the difference. Perhaps, Greek has one too (buried in the dust of history) and maybe not. To me, this is what makes the Babel story interesting! That is, on the surface, everything may not have a clear and logical explanation while the root cause is actually pretty simple.
In spanish the construction "the...this" is used informally. Or when you're angry with a person, you can say "what's the matter with the guy that?" instead of "that guy". It can be found a lot in the Mortadelo comics, where the characters always say "the guy that", "the house that"... In this example you can read "prepare el gas ese" (prepare the gas that): https://rosesblog.files.wordpress.com/2007/07/tira-mortadelo-2.jpg
Koine Greek seems to have it but not in the same order (it looks like Spanish or Romanian). For example, some New Testatment versions have: τη πόλη ταυτή (this city), see Matthew 10:23 and την γενεάν ταυτήν (this generation), see Matthew 11:16. NOTE: the accents are not properly placed...