As determined by law since 1984, Luxembourg has only one national language, which is Luxembourgish. It is considered to be the mother tongue or "language of the heart" for Luxembourgers and the language that they generally use to speak or write to each other. Luxembourgish is considered a Franconian language specific to the local population which is partially mutually intelligible with the neighboring High German, but which also includes more than 5,000 words of French origin. Knowledge of Luxembourgish is a criterion for naturalisation.