An e-mail of Stefan Löffler from the TeXworks team was forwarded to me. Translated into English it says:
I want to start by saying that the version of TeXworks, which is
included in TeXLive (and other TeX distributions), is sometimes
modified (for example, to adapt the paths to the respective
distribution). [...] Yes, TeXworks supports [.dic and .aff] file
formats (with the hunspell library). [...] Typically, the files
should be installed into the resource folder of TeXworks. By default
C:\Documents and Settings\<username>\TeXworks\ (see
but as mentioned, I suppose TeXLive moved it elsewhere. From the
comments on http://code.google.com/p/texworks/wiki/SpellingDictionaries
I deduce that it is
C:\TeXlive2011\texmf-config\texworks\ (i.e., the
dictionaries should be placed into
C:\TeXlive2011\texmf-config\texworks\dictionaries). To be safe, you
can try the menu item "Scripts > Scripting TeXworks > Show Scripts
Folder" and then navigate to the parent folder.
TW_DICPATH environment variable is only supported on Linux.
Please also note that you must restart TeXworks to update the
ad 1.: Yes, it is possible to use those dictionaries.
For TeXlive2011 portable:
To find out where to place the dictionaries, in TeXworks call
Scripts > TeXworks skripts > show scripts directory (or whatever the menus are named in English).
In that directory create a subdirectory dictionaries and copy the dictionaries in that
C:\TeXlive2011\texmf-config\texworks\dictionaries, depending where TeXlive was installed.)
For TeXlive2012 portable:
In TeXworks call
Scripts > TeXworks skripts > show scripts directory (or whatever it is in English).
Go to its parent directory. There should be directories "completion", "configuration", "scripts" (of course), "translations", and "TUG" inside. In that directory create a subdirectory "dictionaries" and copy the dictionaries in that dictionaries directory.
C:\TeXlive2012\texmf-config\texworks\dictionaries, depending where TeXlive was installed.)
For current, non-portable TeXworks ChrisS provides the correct answer at
ad 3.: Exit TeXworks. When the programme is started again, the dictionaries should be available.
Go to the menue "Edit > Options > Editor > Language for spell check" and choose a language.
Go to the menue "Edit > Spell check" and choose a language.