These languages will come in handy when researching your ancestors from the Netherlands.
Not surprisingly, most records in the Netherlands have been written in Dutch.
During the French occupation (1795-1813), most government records were written in French, including early civil registration records.
During World War II (1940-1945), the Netherlands was occupied by Germany so some official records created at that time were in German. Also, in some parts of current-day Limburg, people originally spoke German so some of the early civil registration records there are in German.
Roman Catholic church records (baptisms, marriages, burials) are typically written in Latin. If you’re researching Catholic ancestors in the period before 1811, you will need these Latin records. If you are lucky enough to trace your family back to the Middle Ages, you will also need Latin if you want to study the earlier charters.
Modern Dutch is different from old Dutch. The language used before say 1700 (called Middle Dutch) is so different from modern Dutch that most people today cannot understand it even if the record is transcribed into legible script.
In the province of Friesland, many people speak Frisian. Since 1985, both Frisian and Dutch are recognized as official languages by the Dutch government and both are used to create official records. Older records will typically be in Dutch, although some newspaper accounts may be in Frisian.
Few if any of the records you will need are in English, but many people in the Netherlands speak English. You can use English to ask questions to archives, genealogists or historical societies. Some archives and municipalities have English versions of their websites.