Set the CSL item language so non-English titles aren't wrongly title-cased

[robin-morand]

Problem

On a journal whose name is not in English, the "How to cite" block (and every
citeproc-rendered citation) title-cases the journal name incorrectly. Example, a French
journal named "Revue suisse de pédagogie spécialisée" is rendered as:

… (2026). Revue Suisse De pédagogie spécialisée, 16(02), 2-8. https://doi.org/…

Note the wrongly capitalized particle "De" (and "Suisse"). The stored journal name is
correctly lower-cased; the capitalization is introduced at render time.

Root cause

getCitation() builds the $citationData object but never sets the item language.
When the item has no language, citeproc-php assumes English and applies English
title-casing (text-case="title", used by APA/most styles on container-title). Per the
CSL spec, title-casing should only apply to English-language items — so the real fix is to
tell citeproc the item's language.

Fix

Set $citationData->language from the publication locale (falling back to the context
primary locale), normalized to a BCP-47-ish form (fr_FR → fr-FR), before the
type-specific branches so it applies to articles, books and chapters alike:

$citationData->language = str_replace('_', '-', (string) ($publication->getData('locale') ?: $context->getPrimaryLocale()));

With a non-English language, citeproc no longer applies English title-case and the stored
casing is preserved for French/German/Italian/… journals. English journals are unaffected
(their locale is en*, so title-casing still applies as before).

How to reproduce / test

1. Create/have a journal whose name contains a lowercase particle, e.g. "Revue suisse de …"
   or "Schweizerische Zeitschrift für …", with a non-English primary locale.
2. Open a published article → "How to cite". Before: "Revue Suisse De …". After: "Revue
   suisse de …".
3. Verified on OJS 3.5.0-4 (APA default style, fr_FR journal): the container-title casing is
   preserved, English journals unchanged.

[asmecher]

Thanks for the detailed filing, @robin-morand! Tagging @kaitlinnewson for a look.