Problems with TexStudio 2.7 spell checker
Did you set the standard language to "en_GB" or "en_US" ? Please check under "options/configure TeXstudio/General" in section "Dictionaries"
You can set the default dictionary "options/configure TeXstudio/General". This will be used for all files (if you do not choose one of the options below to override it).
You can select the current dictionary of a file via the language selector in the status bar. This is a per-file setting and is not stored when closing the file.
You can use a magic comment
% !TeX spellcheck = en_US
to permanently assign a dictionary to a file. TeXstudio checks for this comment when loading a file and automatically sets the current dictionary for the file accordingly.