Colloquial and dialectal German, unlike the standard language, are also partially pro-drop; they typically allow deletion of the subject pronoun in main clauses without inversion, but not otherwise.

Is German a null subject language?

Null subjects in non-null-subject languages

Other languages (sometimes called non-null-subject languages) require each sentence to include a subject: this is the case for most Germanic languages, including English and German, as well as many other languages.

Is Russian pro-drop?

For further information I'd recommend you to checkout the last link, but to sum it up: Russian is a pro-drop language, but less pro-drop that Japanese or Spanish. There are some reasons for this, one of most notable is lack of information we can get from verbs in past tence.