dutch "Simultaan"

The dutch translation to "Simultaan" does not have plural form in spoken lg, thou in theory simultanen could be right.
But to me 'simultanen' sounds pretty odd. Simultaans is wrong and though I think I heard it once.
Just use the simple form "Simultaan". And if you really want to use plural : use "simultaan sessies".
Some words have no plural or no simple form, and this different across all languages.

http://www.vandale.nl/opzoeken?pattern=simultaan&lang=nn#.VZcLyPntlBd does give "simultaans" as the plural and I've heard it many times myself. You're right that there are words that are difficult to translate that way and that "simultaan sessies" is a possible solution (although maybe the two words should be written as one word).

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"Simuls"

Problem solved.