Wikibooks.org is a community for creating a free library of educational textbooks that anyone can edit. The Wikibook's Languages of Europe category can serve, for the language learner, educator and enthusiast, as an enormous doorway into the many European languages, both living and historical.
The European subcontinent has birthed and/or attracted an enormous variety of languages from many sub-branches of what linguists call the Indo-European languages.
Below you'll find direct links to a wide variety of European language open-content textbooks. These are free and open source, for everyone to use and benefit from. And collaborate on - especially language educators who have the knowledge to share with all through this open medium.
To boot, Wikibooks.org itself is available in a wide range of world languages!
Wikibooks Category: Languages of Europe
From Wikibooks, the open-content textbooks collection
These language books concern Languages of Europe. See also Subject:Languages of Europe.
European Languages with Books or Pages
Albanian, Aragonese, Armenian, Austrian, Basque, Belarusian, Breton, Bulgarian, Catalan, Chechen, Croatian, Danish, Galician, Gothic, Greenlandic, High Icelandic, Hungarian, Høgnorsk, Icelandic, Insubric, Irish, Italian, Latvian, Leonese, Lowland Scots, Macedonian, Manx, Neapolitan, Norwegian, Old Church Slavonic, Polish, Provençal, Romanian, Russian, Serbian, Sicilian, Silesian, Slovene, Swedish, Turkish, Ukrainian, Welsh
This may be incomplete when you read this. Please check the Languages of Europe page for the latest content.
European Language Wikibooks Subcategories
Scottish Gaelic language
Visit Wikibooks.org on Languages of Europe.
Wikipedia.org also has a category on Languages of Europe.