lang attribute does not affect spellcheck language

Phenomenon

The lang attribute on a contenteditable region does not affect the spellcheck language in Safari. Spellcheck always uses the browser’s default language, regardless of the lang attribute value.

Reproduction example

1. Create a contenteditable div with lang="fr" and spellcheck="true".
2. Type French text.
3. Observe whether spellcheck uses French dictionary.

Observed behavior

• In Safari on macOS, the lang attribute does not affect spellcheck.
• Spellcheck always uses the browser’s default language.
• Multi-language content cannot be properly spellchecked.

Expected behavior

• The lang attribute should control the spellcheck language.
• Spellcheck should use the appropriate dictionary for the specified language.
• Multi-language content should be properly supported.