From MozillaZine Knowledge Base

language packs

To my experiences this error occurs often when using non-english versions. (re)installing the en-US language pack (langenus.xpi), switching to en-US and back to your own language often helps then. Perhaps that could be added to the page --Sjo 17:28, 24 January 2007 (UTC)

Can you point to any forum threads where doing this solved the problem?--Np 18:38, 24 January 2007 (UTC)

It's problem number 1 in the German Mozilla FAQ [1]. --Jan 10:56, 2 May 2007 (UTC)

What application are you talking about ? The Mozilla Suite or Seamonkey ? Firefox doesn't use langenus.xpi anymore (eg Fx 1.5.0.9 win32 xpi dir). --CrazyFred 13:36, 26 January 2007 (UTC)