Gary’s suggestion to load an alternate language dictionary into the custom dictionary file is useful, but the problem is that then your custom additions will no longer be kept in a separate place, instead being scattered throughout an enormous file. I think a better solution is to combine the .DIC files for all the languages of interest into a single file, name it something else and place it into the C:\Users\myusername\AppData\Roaming\eM Client\Dictionaries folder. You will also have to similarly combine the .AFF files for the same languages (only leaving one “SET ISO8859-1” line at the top of the resulting file and excluding it for the subsequent languages). The .AFF file must be named the same as the .DIC file. I have done this, and it seems to be working out perfectly for me so far. Then, restart EM Client and select the new, combined “language” on the spell check languages menu. The net effect of this workaround is exactly what you would expect to see if EM Client had the option to set multiple spell check languages.