<xsl:param name="language">de</xsl:param>

and access the strings like this

<xsl:value-of select="$AllTexts/{$language}/searchButton"/>

Is there any easy way of making it work other than creating a complete
choose/when/ with static language selection?

Use:
<xsl:value-of select="$AllTexts/*[name()=$language]/searchButton"/>

Regards,
Ragulf Pickaxe :-)

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