GNU Image Manipulation Program without installation.
Download Portable GIMP 32-64 bit Multilingual (63 MB)
Extract and run GIMPPortable.
Copy additional fonts in Data\GIMP\fonts
To change language, add GIMPLanguage=(one of the subfolders names in \App\GIMP\share\locale) in GIMPPortable.ini
If you drag'n drop a file on (or open with) GIMPPortable: it will be opened in GIMP.
Settings of installed GIMP should be preserved.