According to the constitution, Turkish is the sole official language and no other languages can be used in government offices and municipalities.

The accused include Osman Baydemir, one of Turkey's most popular Kurdish politicians and the mayor of Diyarbakir, the main city in the Kurdish-majority southeast.

The other politician charged is Abdullah Demirbas, who was removed last month from his post as mayor of Sur, Diyarbakir's multi-ethnic old town, after the city council in January allowed the use of Kurdish, Armenian, Arabic, Assyriac and English in municipal services.

The charge sheet accused the defendants of "abuse of office" and sought prison sentences ranging from one to three years.

The trial of Baydemir, Demirbas and the 17 city councilmen who voted for the municipal bill is scheduled to begin on November 7.

Diyarbakir's governor, Ankara's top representative in the area, has asked a district court to scrap the multi-lingual service.

Anakara has in recent years -- under European Union pressure to improve its human rights record -- legalised broadcasts in Kurdish and allowed private institutions to teach the Kurdish language.

The law, however, still requires Kurds to use solely Turkish, the only official language, in official communications and politics.

Kurdish activists insists that Kurdish should be taught in schools and used in all spheres of public life.

Ankara fears that broader Kurdish cultural freedoms may embolden the armed separatist campaign of Kurdish rebels fighting the central government since 1984. The conflict has claimed more than 37,000 lives.