How to add a language to gtkspell

[Johan Spee]

I use gtkspell in combination with sylpheed. I can choose from 20 different English dictionaries that, apparently, come with the package. I would like to add Dutch (just 1 will do), but have no idea how this can be done. Note that I do not want to make the entire OS bilingual - I just want to enable gtkspell to use the Dutch language.

thanks,

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Johan Spee