Are you sure Dutch is missing? The Windows Desktop FBReader (at least) includes Dutch as an option for the default language. I assume it will therefore hyphenate Dutch.
There are other possibilities:
- The ebook's language code metadata may not be specifying Dutch correctly.
- FBReader may not be recognizing the language code metadata, even though it is correct. This turns off FBReader's hyphenation.
- The ebook's language code metadata may be set to UND (or und), for undefined. This turns off FBReader's hyphenation.
I suggest opening a Dutch ebook in Desktop FBReader (Windows or Linux) and see what it auto-selects as the language. It it does not select Dutch and/or does not auto-hyphenate, then attach (or provide a pointer to) a public domain ebook illustrating the problem.