How do we know that a language is compliant to dot net??????

There is a set of rules known as the Common Language Specification (or CLS) which a language needs to satisfy to be .NET compliant.

These rules guarantee that the language supports the minimum set of features needed to ensure that it can produce or consume types which are compatible with other CLS-compliant languages.

Please see this link (http://msdn.microsoft.com/en-us/library/12a7a7h3.aspx) for further details.