Ancient Mew was the same language during every release. Actually, each symbol on the card represents a letter in the English alphabet, so I wouldn't really say that it is a different language. It's more like an alternate (seemingly unreadable) font.
For instance, take the information that you know (Mew, Weakness, Resistance, Retreat Cost, and New Species). This will allow you to identify several symbols from the card (M, E, W, A, K, N, S, R, I, T, C, O, and P). Apply each of these letters to the parts of the card you have yet to translate.
Attack: PS_C_E
Other text: _ITT_E _O_... __ E_I_
The official translation for the attack is "Psyche" and the extra text is "Little god... or evil."
Of course, some of the letters seem to be written differently. Another case, perhaps?
The number system could come from an ancient culture, though.
(I got my Ancient Mew from Pokemon the Movie 2000.)
Still a pretty cool looking card, but I wouldn't give over $5 for one.