I've noticed that, not only in Russian, but in many other Eastern European languages that in French loanwords that end in "-tion", the suffix almost always appears as "-cija" (-ция). Examples include words like "informacija". I've tried to look up the etymology of the suffix to no avail.
My question is, is "-cija" a native Slavic suffix or is it a phonetic rendering of the original French suffix?
"-ция" is a rendering of Latin "-tio" rather than French "-tion". Even though some words were borrowed from French (actually in Russian many loan words were borrowed indirectly through Polish), they became "Latin"-lookalike in Russian.
Just to complement Matt's answer. Your assumption is indeed false, first set of words with "-ция" was not derived from French words but rather from their Latin cognates - through Polish - for instance words навигация, революция, нация, милиция, конструкция, акция are corresponding to Polish nawigacja, rewolucja, nасjа, milicja, konstrukcja, akcja.
Then some words were derived from French (or English which was influenced by French and also have -tion) but the tradition to keep "-ция" for "-tion" preserved.
As of why Latin -tion morphed into cja - it's better ask at Polish-related Stack. Which, unfortunately, does not exist so far.
