@Shiny You do see what the writing system looks like in the light novel too (when Myne is sitting on Fernidad's lap reading, it also shows the book). In that case, the writing system actually looks kind of like a mix of Arabic and Hebrew.
As far as the original question goes, I'd assume the language sounds pretty German/Austrian since so many of the words are German-based. I don't think we can really make a good guess as to a time period since there really is no reason why the German language of 1,000 years ago could be the language of today and 1000 years ago German sounded completely different.
Languages tend to change by incorporating exterior languages into their syntax and vocab (one of the reasons English is such a cluster F is because of the long history of various countries and tribes conquering Britain) on top of just slightly changing from generation to generation. So, in that sense, you would probably have to know the geopolitical history of the nation that Efre (whatever the spelling) belongs to as well as what their neighbors' languages were like.
TL;DR - Probably vaguely German, but no real way to compare to RL.
