How to install a dictionary (danish) in Texmaker
Step one is to download a dictionary, if you haven't done that already. The dictionaries are the same kind used by LibreOffice, OpenOffice and others, and can be downloaded from e.g. http://archive.services.openoffice.org/pub/mirror/OpenOffice.org/contrib/dictionaries/ The Danish one is da_DK.zip.
After downloading, unzip the archive, and place it somewhere convenient. It doesn't really matter where you place the files, I think.
To activate the dictionary in Texmaker, go to Options --> Configure Texmaker, and look under the Editor page. In the middle there is a field called Spelling dictionary. Click the folder icon next to it (highlighted in screenshot) to browse for the files you just downloaded and unpacked. Among the downloaded files there is one called da_DK.dic, which is the one you want. Click OK, and you're done.
Updated Dictionary Link
The new working link for acquiring Danish Language can be found on Apache OpenOffice Extensions. Just unpack the .oxt file as an ordinary ZIP file.
Linux (Ubuntu) users must
download the dictionary for English spelling check, download
en_GB
then unZIP it and copy it to along with complete path at/user/share/texmaker/en_GB.dic
.Go to Options --> Configure Texmaker --> Editor --> spelling dictionary and provide complete path where unzipped dictionary file with
.dic
extension is present. Now for spelling checking open your TeX file and press Shift+Ctrl+F7 you will see all word with spelling mistake would be underlined with red color.