Translating CiviEvent Public pages
All those strings should be in transifex (and compiled in the .mo files).
Please keep in mind that the string might contains HTML and what you see as one big paragraph on the screen might be in fact be a concatenation of several strings.

For example, your first example is in fact 2 separate strings in transifex (and the second one contains HTML) :

    $statusMessage = ts("It looks like you are already registered for this event. If you want to change your registration, or you feel that you've gotten this message in error, please contact the site administrator.") . ' ' . ts('You can also &lt;a href="%1"&gt;register another participant&lt;/a&gt;.', array(1 =&gt; $registerUrl));


You can find those string (for fr_CA) here :


https://www.transifex.com/civicrm/civicrm/translate/#fr_CA/event?q=It looks like you are already registered for this event
https://www.transifex.com/civicrm/civicrm/translate/#fr_CA/event?q=register another participant


If after looking in transifex, you can't find the strings, it might be three different problems :


there is a missing ts (translation function) in the code, meaning there is bug that should be mentioned in the issue tracker (gitlab)
the string is a new one or has been changed and transifex is not yet up-to-date
there is bug with the string extractor


Once you have updated the string in transifex, you need to extract po files and compile them or wait for the automated process to compile them for you (once a day) -> http://download.civicrm.org/civicrm-l10n-core/mo/fr_CA/civicrm.mo (replace fr_CA by your locale)