1. Your updated JS hasn't been approved yet. Your edits won't take effect outside of test mode until it is approved.

2. You have mistakes in your CSS that are causing the navigation buttons to not display correctly.

Example from FR CSS:

.portal_slide.portal_buttons.portal_homelink {
    float: left;
    width: 35px;
    height: 35px;
    background-image: url("//onepiece.fandom.com/fr/wiki/Special:FilePath/Slider menu.png");
    background-size: cover;
    cursor: pointer
}

Same portion from EN CSS:

.portal_slide .portal_buttons .portal_homelink {
    float: left;
    width: 35px;
    height: 35px;
    background-image: url("/wiki/Special:FilePath/Slider_home.png");
    background-size: cover;
    cursor: pointer
}

Edit: I am just curious, how long ago did you start asking for help with this issue from your other sources of help? Seems odd to me they would be able to help you get this far but not catch something like this.

Edit 2: Also, please remember to always give a link (example) to the wiki when asking for help with something like CSS/Lua/JS. Don't assume we just know the wiki or will be able to search for it. Even better if you can give us links directly to the template/code in question rather than making us search your wiki for it.

> I've seen same type of Urls in another MediaWiki page on my wiki so I thinked it'll work too here.

Wikia.css can work if imported on the community CSS (@import).