"Knowledge of the structure and content of a foreign (non-English) language including the meaning and spelling of words, rules of composition and grammar, and pronunciation."
Source: careers.org
A foreign language is a language indigenous to another country. It is also a language not spoken in the native country of the person referred to, i.e. an English speaker living in Japan can say that Japanese is a foreign language to him or her. These two characterisations do not exhaust the possible definitions, however, and the label is occasionally applied in ways that are variously misleading or factually inaccurate. Some children learn more than one language from birth or from a very young age: they are bilingual or multilingual. These children can be said to have two, three or more mother tongues: neither language is foreign to that child, even if one language is a foreign language for the vast majority of people in the child's birth country. For example, a child learning English from her English father and Japanese at school in Japan can speak both English and Japanese, but neither is a foreign language to her A German student learning French." Source: Wikipedia
"It’s estimated that up to 7,000 different languages are spoken around the world. 90% of these languages are used by less than 100,000 people. Over a million people converse in 150-200 languages and 46 languages have just a single speaker!" Source: BBC