Special characters are not allowed to be used in WordPress URLs by default. As a rule, it removes all non-standard characters, leaving just letters, numbers, and dashes.
In the first place, in order to be able to describe how to fix the problem, we need to have a solid understanding of what the problem actually is. Permalink Manager can improve the native permalink system and allow you to use additional special characters in WordPress URL addresses, such as underscore or dot.
Of course, this is done on purpose since various browsers handle non-standard (non-ASCII) characters in URLs differently. The goal was to standardize and maintain compatibility for users of older browsers like Netscape and Internet Explorer. They now make up a small percentage of online visitors, but the procedure for WordPress has not altered.
How does WordPress remove special characters and sanitize slugs?
The non-standard characters are encoded with the "percent-encoding" method and substituted with the hexadecimal equivalent of their ASCII value. WordPress goes even farther by limiting you to ASCII letters, digits, and dashes. It is important to point out that in addition to the aforementioned, all capital characters are changed to their lowercase counterparts automatically.
By default it sanitizes the slugs (post names) with
function. The dots, accents and other non-standard character are automatically removed from native slugs, when the post is saved or updated.
How to allow additional special characters in WordPress URLs?
Permalink Manager, as previously indicated, allows for the use of additional special characters in permalinks. Simply enter Permalink Manager settings, then go to the "Advanced settings" tab and toggle the "Strip special characters from slugs" option.
You may change the sanitization settings to allow dots or underscores in custom permalinks that you wish to manually adjust, as well as to keep them in the new permalinks after the post or page is published. Make sure your "Slugs mode" option is set to "Use actual titles as slugs" instead of "Use native slugs" in order to take use of this feature. Check out the separate article for additional information on this function.
You may manually add dots or underscores to custom permalinks at any time, regardless of the "Slugs mode" you select, as long as the option "Strip special characters from slugs" is disabled. When both options are set, Permalink Manager will use the title for the new default permalink instead of the native slug (where the dots are replaced with hyphens).
How to keep the dots in old permalinks?
If you changed "Slugs mode" and would like to keep the dots inside the permalinks of previously added posts and terms, you will need to regenerate their custom permalinks.
How to keep accented letter in permalinks?
By default, all accented letters in custom permalinks will be replaced with their non-accented equivalent (eg. Å => A, Æ => AE, Ø => O, Ć => C). To deactivate remove_accents() function and keep letters with accents please disable it in Permalink Manager settings: