The World Atlas of Language Structures (WALS) is a large database of structural (phonological, grammatical, lexical) properties of languages gathered from descriptive materials (such as reference grammars) by a team of 55 authors.
This looks like a very interesting resource to learn about languages (e.g. Spanish, Russian), or to learn about the many elements that conform a language (e.g. Chapter Order of Subject, Object and Verb).
There is also an Interactive Reference Tool (WALS program). The interactive database will also contain additional information on languages (genealogical classification, alternative names) and on each language-feature pair (bibliographical reference, example sentence).
ㆍenglish ㆍgeneral ㆍinteresting
Amazonia is now becoming a carbon source. 
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Advanced beginner