With Nav Canada, anyone wishing a transfer to units in Quebec must take an oral French test (ooh er missus) since local traffic will speak only French, and I've heard that Skyguide will only hire people who are fluent in French (for Geneva) or German (for Zurich). In their case, they say that as well as local traffic, some co-ordination and all calls with airport vehicles will be in German. On the other hand, Arabic is not required for controllers in the more friendly parts of the Middle East.