Do the files named .I10n (localisation files) change from (say) 4.6.4 to 4.6.5? Or do they only change with major updates, say 4.5 to 4.6?
The l10n translation files (civicrm.mo files in the l10n directory, distributed in the civicrm-l10n-4.6.x.tar.gz files) should change between versions, however:
The latest translation files always support the 3 last CiviCRM versions. So currently, civicrm-l10n-4.6.5.tar.gz can be used for CiviCRM 4.4.x, 4.5.x and 4.6.x. This was done a while back to avoid having version-specific translation spaces on Transifex.com, while still supporting older versions.
Between minor versions of CiviCRM (4.6.4 to 4.6.5), there can be changes in the code that require us to send new strings to Transifex. For example, if someone fixed a typo in a string, added new strings, etc. We have not been doing that systematically for every release. While the process of pushing strings has become easier, it's still kind of messy, time consuming, because it requires validations to make sure we don't accidentally delete strings, or I find typos in new strings that need to be patched before we can update the strings, etc.
Use l10n update extension to keep them fresh https://github.com/cividesk/com.cividesk.l10n.update