I've had several lesson's giving tonne as a translation of ton and vice versa. This is incorrect. Ton and tonne are different measures.
Ton is an imperial measure with two versions - British (long ton) and US (short ton).
Tonne is a metric measure that is between the two. Although similar weights, in a real world situation you could get in trouble with (say) customs & excise for "short-measuring" if you did not know they are different.
It would probably be better (and I can feel my British patriotism protesting even as I type this) to use the US convention of "metric ton" in the English language versions and "tonne" in non-English sentences.
This has the added benefit of reminding us not to assume that other countries use the same conventions as us.