问题:

I have a Flask/Dash app that uses the Flask-Babel module. The translation works like a charm after logging in and browsing through pages. However, I cannot make it work for the login page which will always be displayed in English. The messages.po and messages.mo both contain the translation strings I prepared for the login page, so the compilation part seems to work fine.

Here's a snippet from my app.py (with a hard-coded choice of Spanish):

import dash from dash.dependencies import Input, Output from flask import Flask, request from flask_babel import Babel # some more imports...  # (...)  def main():      update_dataframes()      app = dash.Dash(         "MyApp",         url_base_pathname='/summary',         static_folder="static",         sharing=True,         csrf_protect=False     )      # Hook Flask-Babel to the app     babel = Babel(app.server)      @babel.localeselector     def get_locale():         # return request.accept_languages.best_match(context.config['LANGUAGES'].keys())         return 'es'      # App layout     app.layout = build_app_layout(context)      # Setup callbacks     setup_callbacks(app)     setup_login(app, app.server, context.config)      # Start Dash/Flask app     app.server.run(         port=context.config['DEPLOY']['SERVER_PORT'],         debug=context.config['DEPLOY']['SERVER_DEBUG'],         threaded=context.config['DEPLOY']['SERVER_THREADED']     )      # Interval tread to update all dataframes     ThreadPoolExecutor(max_workers=1).submit(update_dataframes_thread)  if __name__ == '__main__':     main()

Below, a part of the setup_login(...) method called above. I'd like to notice that app.server is passed to it from the code above, after Flask-Babel has been hooked to the app (don't really know if that matters much):

from dash_flask_login import FlaskLoginAuth from flask_login import LoginManager, UserMixin, login_user, logout_user # (...)  login_app = Dash(     name='login-app',     url_base_pathname='/login',     server=app.server )

What I tried: hooking the Flask-Babel again for the login_app Dash() instance, but that didn't work (anyways it's still the same app.server).

I've come across this SO question with a similar problem, but it seems to be specific to Flask-Security module (not my case).

What am I missing to make the login page translated?

回答1:

Although I haven't found a direct reason why a combination of Dash and Flask-Login don't work with Flask-Babel on the login page, I solved the problem with a workaround - I'm dynamically updating generated HTML component through Dash's callback decorator just after loading the page. The function simply substitutes the original English some_string with gettext(some_string) tag which is detected properly in the callbacks. This way the page loads in English and immediately gets translated, as the callbacks come to action. Minimal example:

app.layout = html.Div(         [             html.H1('Hello World!', id='h1'),             html.Div(html.A('login', href='/login')         ]     )   # Display the message translated to another language @app.callback(     Output('h1', 'children'),     [Input('url', 'search')] ) def translate_message(children):     return gettext('Hello World!')

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