Since 2007 Turkish men or women who wanted to join their spouses already living in Germany have been required to demonstrate basic German language proficiency to move to the country.
The court ruling is the result of a two-year legal battle by the wife of a Turkish businessman living in Germany to be allowed to join him.
In January 2012, the German embassy in Ankara refused again to grant the woman, Mrs Dogan, a visa for the purpose of joining her husband who had lived in Germany since 1998, on the grounds that her German was not good enough.
But on Thursday the EU court ruled that the German language requirement violates agreements Turkey made in the 1970s within the European Economic Community (EEC), the predecessor organization to the EU.
Under the EU-Turkey agreement no new restrictions were allowed to be put on freedom of movement.
The court agreed that the 2007 introduction of the language test sought to prevent forced marriages and to promote integration, but added the test would mean someone might be forced to choose between their work in an EU member state and their family.
The judgment read that the German language requirement was "contrary" to EU law. However, the ruling only affects Turkish people and not the German language test for immigrants.
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