Noticed that there was a style rule in bootstrapbase that wasn't being applied to RTL forums; the intent was to align .lastpost text left under RTL, but it never kicked in due to incorrect nesting (.dir-rtl and .path-mod-forum are classes applied to the same element), see https://github.com/moodle/moodle/blame/master/theme/bootstrapbase/less/moodle/modules.less#L260.
Some minor improvements as well:
- added minor padding on table cells
- lined up Replies header with Replies table cells (header was aligned left, cells were aligned center)
- reduced text size of non-topic cells to make things read a little better