By Imogen Foulkes BBC correspondent in Ostermundigen

Swiss citizenship requires 12 years of permanent residence

Local communities in Switzerland have the major say in deciding who should become Swiss, and can set their own criteria.

About 20% of the country's population is foreign - citizenship requires 12 years of permanent residence, and approval usually involves at least an interview.

Ostermundigen's written tests have many supporters, as language competence among Switzerland's foreign community is a big issue.

But critics of the tests say waiting until someone applies for citizenship before asking about language proficiency is unfair and could lead to serious inequalities in Switzerland's naturalisation process.

'Tool for integration'

I visited a classroom in Ostermundingen where a dozen foreigners are learning German.

You don't become a Swiss citizen if you have a lot of debts, you have to show you are responsible and pay things off regularly Ursula Norton, Ostermundigen town council

Most are women, and most are struggling.

Their goal - to pass the written test. They have to pay for the classes, although the town council will refund some money if they attend them all.

Saibua Gr�del from Thailand says she already has pre-test jitters.

"German is very difficult for me, I don't know that they will test me or ask me, I should be very nervous about this I think, and I don't understand why they do it," she says.

Many other towns are keen to follow Ostermundigen's example, but, immigration specialist Stefanie Gass says waiting until someone applies for nationality before checking their language skills is not the right way.

"We should look how they live all these 12 years in Switzerland, do they have chance to participate, can they go to language classes - what chances have they had for integration in Switzerland," Ms Gass says.

But supporters of the tests see them as a tool for integration.

Tough tests set

Some local communities reject applications for citizenship from foreigners who are on social security, or invalidity benefit.

"You don't become a Swiss citizen if you have a lot of debts, you have to show you are responsible and pay things off regularly," Ursula Norton of Ostermundigen town council says.

The head of the Swiss Government office for nationality, Roland Schaerer, is not entirely comfortable with this sort of thing - but says the Swiss federal system means he cannot interfere.

"The main problem is the local level, it leads to inequality, of course I would prefer just one system, but it will take decades," Mr Schaerer says.

The language tests have aroused controversy as language proficiency is a key to getting on in a new country.