Makefile: update i18n helpers, switch to linkcheck2

[orangecms]

The update is necessary to accomodate for mdbook 0.5.0. The fork is necessary for 0.5.0 as well, because the original is no longer maintained, as it seems.
TODO: Adjust GitHub CI, but that requires the Action to align. See: jontze/action-mdbook#671

[pamolloy]

There is a build error, I assume unrelated? Perhaps we should setup nightly or weekly builds to see if things break?

mdbook build
2026-06-03 18:14:21 [INFO] (mdbook::book): Book building has started
Warning: The mdbook-mermaid preprocessor was built against version 0.4.36 of mdbook, but we're being called from version 0.4.48
Error: Unable to parse the input

Caused by:
    unknown field `multilingual`, expected one of `title`, `authors`, `description`, `src`, `language`, `text-direction` at line 1 column 120
2026-06-03 18:14:21 [WARN] (mdbook::preprocess::cmd): Error writing the RenderContext to the backend, Broken pipe (os error 32)
Error: -03 18:14:21 [ERROR] (mdbook::utils): Error: The "gettext" preprocessor exited unsuccessfully with exit status: 1 status
make: *** [Makefile:9: book] Error 101
Error: Process completed with exit code 2.

[pamolloy]

Trying to run make prepare on my fresh Fedora install leads to the following:

  error occurred: Command "cc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-m64" "-I" "/tmp/cargo-install60Vs0Y/release/build/onig_sys-12f22d6041309ff8/out" "-I" "oniguruma/src" "-DHAVE_UNISTD_H=1" "-DHAVE_SYS_TYPES_H=1" "-DHAVE_SYS_TIME_H=1" "-o" "/tmp/cargo-install60Vs0Y/release/build/onig_sys-12f22d6041309ff8/out/c77b18e714869709-regparse.o" "-c" "oniguruma/src/regparse.c" with args cc did not execute successfully (status code exit status: 1).


warning: build failed, waiting for other jobs to finish...
error: failed to compile `mdbook-i18n-helpers v0.3.4`, intermediate artifacts can be found at `/tmp/cargo-install60Vs0Y`.
To reuse those artifacts with a future compilation, set the environment variable `CARGO_BUILD_BUILD_DIR` to that path.
make: *** [Makefile:15: prepare_i18n] Error 101

[orangecms]

Trying to run make prepare on my fresh Fedora install leads to the following:

  error occurred: Command "cc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-m64" "-I" "/tmp/cargo-install60Vs0Y/release/build/onig_sys-12f22d6041309ff8/out" "-I" "oniguruma/src" "-DHAVE_UNISTD_H=1" "-DHAVE_SYS_TYPES_H=1" "-DHAVE_SYS_TIME_H=1" "-o" "/tmp/cargo-install60Vs0Y/release/build/onig_sys-12f22d6041309ff8/out/c77b18e714869709-regparse.o" "-c" "oniguruma/src/regparse.c" with args cc did not execute successfully (status code exit status: 1).


warning: build failed, waiting for other jobs to finish...
error: failed to compile `mdbook-i18n-helpers v0.3.4`, intermediate artifacts can be found at `/tmp/cargo-install60Vs0Y`.
To reuse those artifacts with a future compilation, set the environment variable `CARGO_BUILD_BUILD_DIR` to that path.
make: *** [Makefile:15: prepare_i18n] Error 101

That would be before my changes though; v0.3.4 is the old version, and I am changing it to v0.4.0?