Thats_PM:
To answer questions 1 and 2, each parent must have a different "language version". For example, if you're playing an English language game, every Pokemon generated in that game will come from an English "language version", regardless of what country the game was purchased in.
Some hints you can use to determine whether a Pokemon comes from a different language version: Some Pokemon have different names in French and German. If you have a Froslass named "FROSDEDJE", for example, or an Infernape named "PANFERNO", the Pokemon is likely to come from a German language version. (Note, however, that Spanish and Italian language games use the English names for Pokemon.) The presence of hiragana and katakana makes it extremely likely that a Pokemon comes from a Japanese language version. Finally, a traded Pokemon from a different language version will earn slightly more Exp. Points than a traded Pokemon from the same language version.
Because of the way the "Masuda method" is applied, the Everstone effect will fail to work properly if both Pokemon come from different language versions. This is because the "Masuda method" overwrites the baby's personality ID (which includes the baby's nature) as it tries to generate a shiny egg.
Many people have different views on what a "legit" or "legal" Pokemon is. In general, though, a "legal" Pokemon is one you've caught yourself, without the aid of any external device.