In Thunar, create a file whose extension will be displayed on two lines. For example (with my settings), "sauvegardes.sh" will be displayed as the following:

    ICON
sauvegardes.s
h

I think it would be visually better to consider dots as separators, so extensions would not be wrapped in the middle:

    ICON
sauvegardes.
sh

Other example: with HTML Purifier library, there's a file named "HTMLPurifier.safe-includes.php". With my settings, it's displayed as the following:

    ICON
HTMLPurifier.s
afe-
includes.php

If dots were considered as separators, the filename would be IMO a lot better wrapped:

    ICON
HTMLPurifier.
safe-includes.
php