(1) Romanian: It seems unlikely that the suffixed/postfixed/postposed definite article in Romanian is a Slavic feature, because most Slavic languages do not have articles at all, much less suffixed definite ones. (Note that the indefinite article is not a suffix in Romanian.)

A suffixed definite article is not at all incompatible with Romanian’s Latin roots. In Latin, word order was very free. In all Romance languages (except Sardinian), the definite article developed out of the demonstrative pronoun “ille”. In Latin, the phrases “ille lacus” and “lacus ille” were semantically and grammatically equivalent, differing only in style. Romanian developed the second variant into “lacul” under influence of the Balkan Sprachbund. See:
http://en.wikipedia.org/wiki/Balkan_linguistic_union#Postposed_article

In sort, the suffixed definite article is neither Latin nor Slavic: it’s Balkanic. 🙂

(2) Maltese: it is hardly surprising it sounds much like Arabic; it is genetically a Semitic language (descended from a dialect of Arabic), although it now has a lot of imports from Italian, Sicilian and English.

(3) Portuguese: The differences between Portuguese spoken in Portugal and Brazil are mostly in vernacular and informal language. Formal written language is virtually identical, with differences comparable to those between British and American English. There is one single Wikipedia for Portuguese like there is for English.