You don't have to speak Dutch to be a professional dancer in the Netherlands, it is important though that you ar able to speak English.
The two major companies are The Dutch National Ballet en the Nederlands Dans Theater.
The Dutch National Ballet
The National Ballet is about the only company to perform classical repertoire like Swan Lake but also Balanchine and repertoire by Hans van Manen.
Nederlands Dans Theater
The Nederlands Dans Theater is well known for repertoire by Jiri Kylian, at pressent you see them perform choreographies by a.o. Lightfoot León, Jacopo Godani, Ohad Naharin and William Forsythe.
Other important companies in the Netherlands are:
Dance Works, Rotterdam (artistic director: Ton Simons)
Galili Dance, Groningen (artistic director: Itzik Galili)
Introdans, Arhnem (artistic director: Roel Voorintholt)
&
Scapino Ballet, Rotterdam (artistic director: Ed Wubbe)