Allow rest parameters to be forced to be non-zero length

Describe the problem

I'm trying to make a multilingual website with localized URLs.
I have been advised to use the following structure:

• [...news=news]
  • [slug]

src/params/news.ts:

import type { ParamMatcher } from '@sveltejs/kit';

export const match: ParamMatcher = (param) => {
    return param === 'news' || param === 'ru/novosti';
};

Expected behaviour:

• /news - News list page in English
• /news/foo - "Foo" news post in English from DB
• /ru/novosti - News list page in Russian
• /ru/novosti/foo - "Foo" news post in Russian from DB
• /ru/news - 404
• /novosti - 404
• /barbaz - 404

Actual behaviour:

• /novosti - "Novosti" news post in English
• /barbaz - "Barbaz" news post in English

If I understand correctly this happens because in the past rest parameters were changed to allow zero-length ( https://github.com/sveltejs/kit/issues/554 ), in which case a corresponding matcher doesn't run on them.

Describe the proposed solution

Maybe allow to specify which rest parameters can have zero-length and which can't?

Alternatives considered

Initially I thought of a simpler solution, but it's currently not supported because there is no way to read already matched "parent" paramerers ( https://github.com/sveltejs/kit/issues/4500 ).

• [lang=lang]
  • [news=news]
    • [slug]

If everything else fails I guess I'll have to abandon the idea of localizing URLs, even though it's nice for usability.

Importance

would be nice to have

Additional Information

No response

Start with the localized route and matcher example in src/params/news.ts, then trace how the rest parameter handles empty and non-empty paths. Define the configuration needed to require a non-empty rest parameter and verify the expected localized and 404 routes from the issue.