i18n_headers seems to not support permalinks with placeholder variables

[GruberMarkus]

The i18n_headers Liquid tag does not seem to support permalinks with placeholder variables, such as permalink: "/blog/:year/:month/:day/:slug/".

In the headers, the permalink is shown as defined in the front matter, without the placeholder variables being resolved to their actual values. It does not matter if the value in the permalink is in quotes or not.

permalink: "/blog/:year/:month/:day/:slug/" results in the literal i18n header href "/blog/:year/:month/:day/:slug/" instead of the resolved one (/blog/2025/10/27/my-own-slug/).

[george-gca]

Where are you defining the permalink? This should be set in the _config.yml file.

[GruberMarkus]

I set the permalink directly in post.

The problem is likely not about where the permalink is defined, but that polyglot does not work with placeholder variables such as ":day".

[george-gca]

Are you sure pure jekyll supports these placeholders in the post front matter? I know that these are supported when you define the permalink in the _config.yml. It this is supported by jekyll, then I agree that it should be also supported here, if not, it should simply replicate the behavior of jekyll.

[GruberMarkus]

Yes, the placeholders work fine when used in the front matter.

[GruberMarkus]

@untra: Do you have an idea how this issue could be resolved?

[untra]

Heya, sorry for the delay in response. This is a niche one:

Jekyll does not fully support permalink placeholders in front matter. This is a known limitation documented in jekyll/jekyll#2475. Placeholders like :year, :month, :day, :slug only work in the global _config.yml permalink pattern, not when set explicitly in a document's front matter.

When you set permalink: /:year/:month/:day/:slug/ in front matter, Jekyll treats it as a literal string and does not resolve the placeholders. This could still be implemented as you're intending, but it touches a little of everything and isn't jekyll standard.

Can I ask what you are trying to accomplish with a variable permalink in the frontmatter? It sounds like you are trying to define a dynamic blogpost permalink, which is neat but why?

[GruberMarkus]

Hm, it works perfectly fine.

The current Jekyll documentation (https://jekyllrb.com/docs/permalinks/#front-matter) is not clear about this. While the placeholder are mentioned in the "Global" section only, it is also only mentioned that built-in styles are not respected in front matter. This may be interpreted as implying that everyting else, including placeholders, works in front matter - and as far I can observe, Jekyll behaves like that in real life.

Yes, I define dynamic post urls because I want individually defined slugs for all languages the post is available in. This is why I define the slug and the permalink referring to the slug in the front matter.