LanguageMenuViewHelper can trigger a caching problem with URL parameters

[ako-3004]

vhs 6.1.2 / TYPO3 10.4.32

Situation:

• Page cache has just been cleared.
• A bot makes the first call with additional URL parameters Then these URL parameters are taken over by the LanguageMenuViewHelper and also end up in the page cache. I found e.g. &utm_source=x parameters in the URLs of the language navi.

Could replicate this on different webs with different VHS and TYPO3 versions. Cause here is the 'addQueryString' => 1 in getLanguageUrl() in ViewHelper.

I wouldn't consider this a bug but an additional difficulty in dealing with the LanguageMenuViewHelper.

I see possible workarounds:

1. the LanguageMenuViewHelper must be called from an uncached plugin.
2. the addQueryString should be set to 0, but then necessary URL parameters from the system must be explicitly allowed.

[NamelessCoder]

You are supposed to use the excludeQueryVars argument on the ViewHelper to list the arguments you do NOT want to append to the URL of each language option. By default, the arguments id,L,cHash are excluded.

See also the section "Excluding GET Parameters from Page Variants" on https://b13.com/blog/caching-in-typo3-part-2-cache-variants-of-a-page-with-chash. You may want to assign the value of $TYPO3_CONF_VARS[FE][cacheHash][excludedParameters] to your template and use this as value of the excludeQueryVars argument for v:languageMenu (this option is designed precisely for various utm_* and similar types of URL parameters).