Language unknown to isodate

Question

I am writing a Dutch article in combination with the British notation for dates.

\documentclass{article}
\usepackage[dutch]{babel}
\usepackage[british]{isodate}

\begin{document}
  \printdate{5/9/2017}
\end{document}

The result is as expected: "5 september 2017". However, the log contains the warning Language dutch unknown to isodate. This message appears for every \printdate, which is really annoying. Changing the order of the packages does not have an effect.

Is this a known problem? Can I safely ignore the warnings?

Answer 1

When isodate detects babel it redefines the internal language name to \languagename so that the dates adapt to the surrounding language. If you really want to force it to always use the british format (which sounds a bit odd if your main language is dutch) you can redefine the language name again:

\documentclass{article}
\usepackage[dutch]{babel}
\usepackage[british]{isodate}

\makeatletter
\AtBeginDocument{\def\iso@languagename{english}}
\makeatother
\begin{document}

  \printdate{5/9/2017}
\end{document}

If you actually want dutch date formats, you should write a dutch.idf along the lines of e.g. the danish.idf.

Answer 2

The complete warning is

Package isodate Warning: Language dutch unknown to isodate.
(isodate)                Using default format on input line 6.

If the output you receive is what you expect, then the "default format" is what you need and you can safely ignore the warning.

If you wish to turn this warning off, you can use the silence package, similar to what is suggested in How do I get rid of particular pdftex warning message?

The documentation mentions it only supports a limited number of languages, but you can add your own language support, or just (re)define the output to suit your needs.