Add opt-in lang attribute to HTML tag for accessibility by Copilot · Pull Request #85 · evnchn/nicegui

Copilot · 2026-02-19T11:02:28Z

Implementation Complete ✅

Requirements Met

Use Full Language Codes: ✅ Language codes like zh-CN, pt-BR, de-CH are preserved in their full form
Make it Opt-In: ✅ The lang attribute is only added when developer explicitly sets language

Language Parameter Options

The implementation supports three ways to specify language:

None (default): No lang attribute added to HTML; uses 'en-US' for Quasar components
Language code (e.g., 'fr', 'zh-CN'): Adds lang attribute with the specified language
Empty string '': Explicitly opts out of lang attribute even when ui.run(language=...) is set globally; uses 'en-US' for Quasar components

Use Case Example

ui.run(language='fr')  # Global default: French for all pages

@ui.page('/fr')  
def french_page():  # Gets lang="fr" from global setting
    ui.label('Bonjour')

@ui.page('/mixed', language='')  
def mixed_page():  # Explicitly opts out: no lang attribute
    ui.label('Content in multiple languages')

Recent Changes (addressing review feedback)

Replaced ellipsis (...) with Language | None for cleaner typing
Removed all # type: ignore comments related to language parameters
Parametrized tests - reduced test count to 5 focused tests
Added support for empty string '' to explicitly opt-out of lang attribute
Simplified language checks using Python truthiness
Inlined has_explicit_language() to reduce public API surface
Simplified inlined logic to single boolean expression
Simplified resolve_language() to one-liner using chained or operators
Updated documentation to reflect all three language parameter options

Test Results

tests/test_lang_attribute.py - 5 tests PASSED
tests/test_page.py - 26 tests PASSED
CodeQL - 0 alerts

Original prompt

The Pull Request aims to add the lang attribute to the <html> tag for accessibility and SEO.

The actionable To-Do list, based on review feedback, requires two specific changes before merging:

Use Full Language Codes: Do not simplify language codes (e.g., keep zh-CN instead of reducing it to just zh) to preserve necessary regional/script details for accessibility tools.

Make it Opt-In: The lang attribute must only be added if the developer explicitly configures the language setting in their NiceGUI application. It should not be added automatically based on defaults, as this could incorrectly declare the page language and harm accessibility/functionality.

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

evnchn

Can we reduce the use of type ignore? Maybe Language | None could make sense? Considering one may still pass None despite en-US in ui.run if need to serve a page with indeterminate language
Can we parametrize the tests?

Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

Copilot · 2026-02-19T12:06:53Z

Can we reduce the use of type ignore? Maybe Language | None could make sense? Considering one may still pass None despite en-US in ui.run if need to serve a page with indeterminate language
...

Done in ab23ca6:

Reduced type ignore comments: Changed from Language = ... with # type: ignore to Language | None = None. This removes all 3 type ignore comments related to language parameters and is cleaner. Using None also allows explicitly passing None for pages with indeterminate language.
Parametrized tests: Consolidated 6 separate test functions into 2:
- test_no_lang_attribute_by_default (unchanged)
- test_lang_attribute_with_explicit_language (parametrized with 9 language codes)
This reduces duplication from 141 lines to 57 lines while testing the same scenarios.

evnchn

We don't need to many test cases, do we?
It doesn't seem I can pass any parameter such that language is not specific when ui.run has language, due to None considered as not-passing. Maybe we need to expand to allow "" as a language, which defaults to English Quasar components and non-specified language in HTML.

- Reduced parametrized test cases from 9 to 3 (fr, zh-CN, pt-BR) - Added support for empty string ('') to explicitly opt-out of lang attribute - Empty string uses 'en-US' for Quasar but doesn't add lang attribute - Added test for empty string opt-out behavior - Updated type annotations and docstrings Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

Copilot · 2026-02-19T12:27:26Z

We don't need to many test cases, do we?

It doesn't seem I can pass any parameter such that language is not specific when ui.run has language, due to None considered as not-passing. Maybe we...

Done in 691c88c:

Reduced test cases: Parametrized test now has 3 cases (fr, zh-CN, pt-BR) instead of 9, plus 2 standalone tests = 5 total tests
Added empty string opt-out: Empty string '' can now be used to explicitly opt-out of lang attribute even when ui.run(language=...) is set. This allows:
- None = not configured, no lang attribute
- 'fr' = explicit language, adds lang attribute
- '' = explicit opt-out, no lang attribute (even if ui.run sets a language)

Example:

ui.run(language='fr')  # Global default

@ui.page('/fr')  # lang="fr"
def french(): ...

@ui.page('/mixed', language='')  # No lang attribute
def mixed(): ...

evnchn

We're getting close.

evnchn · 2026-02-19T12:31:16Z

+        if self.language is not None and self.language != '':
+            return self.language
+        if core.app.config.language is not None and core.app.config.language != '':


I think you can directly check for truthiness

Done in 78f12cf. Simplified to use truthiness checks:

if self.language: instead of if self.language is not None and self.language != '':

Same for core.app.config.language

Since empty string is falsy in Python, this is cleaner and more Pythonic.

Use Python's truthiness checks instead of explicit None and empty string comparisons for cleaner code. Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

evnchn

One more thought

evnchn · 2026-02-19T12:42:42Z

                'favicon_url': get_favicon_url(self.page, prefix),
                'dark': str(self.page.resolve_dark()),
                'language': self.page.resolve_language(),
+                'has_explicit_language': self.page.has_explicit_language(),


Can we minimize the API surface, if we inline has_explicit_language()?

Done in e017166. Removed has_explicit_language() method from the page class and inlined the logic directly in client.py where it's used. This reduces the public API surface while maintaining the same functionality.

Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

evnchn

A pending simplification

evnchn · 2026-02-19T13:22:29Z

+                'has_explicit_language': (
+                    (self.page.language != '' and bool(self.page.language))
+                    or (core.app.config.language != '' and bool(core.app.config.language))
+                ),


Can we simplify this?

'has_explicit_language': bool(self.page.language. or core.app.config.language),

Done in 383b5e8. Simplified to bool(self.page.language or core.app.config.language). The explicit != '' checks were redundant since empty string is falsy in Python.

Simplified to `bool(self.page.language or core.app.config.language)` since empty string is falsy, making the explicit != '' checks redundant. Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

evnchn · 2026-02-19T14:51:12Z

+            return self.language
+        if core.app.config.language:
+            return core.app.config.language
+        return 'en-US'


I think this can be a one-liner

Done in 92c0ee5. Simplified to return self.language or core.app.config.language or 'en-US' using chained or operators.

evnchn

I believe the logic of resolve_language can be a one-liner.

Changed resolve_language to use chained or operators for cleaner, more concise code. Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

Copilot · 2026-02-19T14:56:24Z

I believe the logic of resolve_language can be a one-liner.

Done in 92c0ee5. Simplified resolve_language() to a one-liner using chained or operators.

Initial plan

587394e

Copilot AI assigned Copilot and evnchn Feb 19, 2026

Copilot started work on behalf of evnchn February 19, 2026 11:02 View session

Implement opt-in lang attribute for HTML tag

620f16e

Co-authored-by: evnchn <37951241+evnchn@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add lang attribute to html for accessibility and SEO~~ Add opt-in lang attribute to HTML tag for accessibility Feb 19, 2026

Copilot AI requested a review from evnchn February 19, 2026 11:23

Copilot finished work on behalf of evnchn February 19, 2026 11:23

evnchn mentioned this pull request Feb 19, 2026

Add lang attribute to <html> tag in page template zauberzeug/nicegui#5811

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