Abandoned, use xmllint instead, e.g.:
apk --no-cache add libxml2-utils
wget https://raw.githubusercontent.com/symfony/translation/v4.1.1/Resources/schemas/xliff-core-1.2-strict.xsd
xmllint --schema xliff-core-1.2-strict.xsd --noout $(find localPackages -name '*.xlf')Where localPackages is the folder containing your custom code.
Old description:
Symfony provides a translation package which delivers an XLIFF-Linter.
This packages provides a binary wrapper to lint xliff files using this linter.
Just require the package and call ./vendor/bin/xlifflinter <folder|file>.
All further information are available in official documentation of symfonies translation package: https://symfony.com/doc/current/translation/lint.html