The geography of Tunisia has played an important role in its development.

There's no time marker in this sentence, so I feel it's better with 'has played' because the time period is 'throughout it's history, up until now'

For centuries, Tunisia has been at the crossroads of thean ancient civilization.

I'm not sure, because my history and geography knowledge is very bad, but I think there were several ancient civilisations, so if you were to refer to 'the ancient civilisation', it would suggest there is only one. You could say 'an ancient african civilisation' or 'an ancient roman civilisation'

99% of Tunisians practice Sunni Islam, which shapes their cultural traditions.

For centuries, Tunisia has been at the crossroads of the ancient civilizsations.

I assume Tunisia fell between many different groups, who all crossed through it. Hence, use plural "civilisations".
Also, for British English, use "s" instead of "z".

99% of Tunisians practicse Sunni Islam, which shapes cultural traditions.

In British English, "practice" is a noun, while "practise" is a verb.

The vast majority of Tunisians speak Arabic, andbut French retains an important place in education, business and tourism.

Using "but" emphasises that although Arabic may be more common, French is surprisingly widespread. This is appropriate because you continue to talk about French/France in the next sentences.

(This is all extra nuance though, sentence is already perfect!)

The countryunisia is one of the world's largest producers of olive oil, and the desert still hides oil and gas reserves that fund the country.

Perfectly correct sentence, but for slightly better flow avoid repeating "the country" twice.