How are you creating the cached pages?

Standart System Cache -> ON - Conservative caching
Platform Specific Caching - OFF

First test:
Cache Handler - File
Second test:
Cache Handler - Redis

Both fail?

Both fail?

Yes, same problem in both variants. I checked hosting version, then local server backup version. Same result in 2 different servers - text without translation. If I'm turning off "Standart System Cache" then all working right - I have translated JavaScript strings.

I can replicate this. Here were my steps:

• turn on caching selecting Conservative
• edit the module menu layout and added \Joomla\CMS\Language\Text::script('MOD_MENU_FIELD_TAG_ID_LABEL');
• Checked the string in the browser with Joomla.Text._('MOD_MENU_FIELD_TAG_ID_LABEL') and got back MOD_MENU_FIELD_TAG_ID_LABEL

Worth noting that the cached file contains the translated strings but those are not added to the JSON object thus not available in the browser:

Interesting, Script Options works as expected, and Text not, but it also part of ScriptOptions.

To reproduce use following PHP, in components/com_content/src/View/Article/HtmlView.php in display():

Text::script('JYES');
$this->document->addScriptOptions('yes', 'Yes');
$this->document->getWebAssetManager()
    ->addInlineScript('console.log(Joomla.getOptions("yes", "nope") + " " + Joomla.Text._("JYES", "Nope"))', [], ['type' => 'module']);

And check browser console:
Expected: Yes Yes

After cache enabled:
First request: Yes Yes
All following requests: Yes Nope

@Fedik I think the merge should be deep by default (now iirc is shallow replace)

Which merge do you mean?

Called here:

It already use array_replace_recursive

I do not find problem in mergeHeadData() it do not called for me, at all.
Hovewer setHeadData() set all corectly, and then all gone.

Ah, I know, it do not restore Text::$strings, it stay empty,
and any further call of Text::script(), override everything in scriptOptions.

hmhm

I think the mergeHeadData needs also the code for passing the text to script options:

Nope, that should be deleted in future, it not in use.
I have some ideas, need to test.

it not in use.

Well, well, well:

It just a trash in the cache, it not used later ?
You can ignore that. I will do some test and will make a PR.
If I right, the probblem in the Text class.

I'll bet my money here:

How much? ?

100 EUR ?

I will send you my Bank account info ?

Please test #41543