Twig

The filters are registered when Twig is installed.

Without a locale, both use the current locale — that of the request — and give an empty string for null.

Escaping

typography escapes its input first unless it is marked safe, then fixes it as HTML. A string from a visitor stays text: its <script> is shown, not run. HTML the application trusts is marked safe before the filter — with |raw, or because a filter such as ujo_html or markup_html returned it safe — and keeps its markup:

{{ comment.text|typography }}                 {# escaped, then fixed #}
{{ article.bodyHtml|raw|typography }}         {# trusted HTML, fixed #}
{{ article.body|ujo_html|typography('fr') }}  {# safe output of another filter #}

The fixers only rewrite text, so what typography returns is as safe as what it received.

typography_text treats its input as plain text — tags are characters — and its output is escaped by Twig like any string; use it for titles, attributes and other places where markup has no meaning:

<title>{{ page.title|typography_text }}</title>
<img alt="{{ image.caption|typography_text }}" src="…">

The locale of a template

Without a locale, the filters ask Symfony's LocaleSwitcher for the current one: the locale of the request, as the router and LocaleListener set it, or the locale LocaleSwitcher::runWithLocale() switches to, in a command or a message handler that renders an e-mail in its reader's language. Outside a request, the switcher gives the kernel's default locale. Without the translator, symfony/translation, there is no switcher and the filters use default_locale.

{{ article.body|raw|typography }}   {# the locale of the request #}

$html = $localeSwitcher->runWithLocale('de_CH', fn (): string => $twig->render('mail.html.twig', $context));

A text whose language is not the page's passes its own, which always wins:

<blockquote lang="en-GB">{{ quote.text|typography_text('en_GB') }}</blockquote>