Mendeley problem displaying URL visiting date with Biblatex

Question

I'm using Mendeley to create a .bib file for my LaTeX file (I'm using BibLaTeX). In Mendeley I define the field "Date Accessed" for a Web Page as, for example, 18 Sep 2015, so it automatically becomes 2015-09-18. When I export to .bib, it shows urldate = {2015-09-18}. However, when compiled, the bibliography shows "visited on 09/18/2015" (18 is a month that doesn't exist!!).

Strangely, there are other entries that are correct, but I set them exactly the same way, so I'm very confused. In this case, the .bib file shows the urldate in the format {yyyy-dd-mm}, but the output is how I want it (dd-mm-yyyy).

I also tried to force writing in Mendeley 2015-18-09, so that it is the format that BibLaTeX wants, but in that case I get an error saying that the date format is wrong.

Below, you can find an example that shows the correct date (4th Sep 2015) and one that shows the wrong date (18th Sep 2015). Both of them have been input in Mendeley exactly the same way.

@misc{Latitude,
author = {Wikipedia},
file = {:Users/nuri/Library/Application Support/Mendeley Desktop/Downloaded/2e0d0e2cfa61da92bdfb0de9a0276aef68d1ef5b.html:html},
month = sep,
title = {{Latitude}},
url = {https://en.wikipedia.org/wiki/Latitude#Geocentric_latitude},
urldate = {2015-04-09},
year = {2015}
}
@misc{LatLonAlt,
author = {{H. Dana}, Peter},
file = {:Users/nuri/Library/Application Support/Mendeley Desktop/Downloaded/d44961957a5998c59a16ca94005b2ac1a1d715ea.html:html},
institution = {Department of Geography, University of Texas},
month = dec,
title = {{Coordinate Systems Overview}},
url = {http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html},
urldate = {2015-09-18},
year = {1999}
}

I know this question is more related to Mendeley, but I just cannot find the answer anywhere. Any help will be appreciated.

Answer 1

In the end, I solved the problem by adding the British babel package as suggested, and deleting and adding again some of the entries in Mendeley that had problems with the date no matter how many times I tried to change it.

\documentclass[11 pt, oneside]{report}
\usepackage[british]{babel}
\usepackage{csquotes}
\usepackage[backend=bibtex, citestyle=ieee, bibstyle=ieee]{biblatex}
\addbibresource{library.bib}

\begin{document}

\printbibliography[heading=bibintoc]

\end{document}

Thank you for your contributions.

Answer 2

The input format for all date fields in biblatex is always yyyy-mm-dd (with leading zeroes).

So your two urldates are 9 April 2015 for Latitude and 18 September 2015 for LatLonAlt.

You get an output of MM/DD/YYYY, which is biblatex's default for the American locale; the american localisation is also loaded if you don't specify a language or use english.

To change the date format you can switch language with babel to british or australian if you happen to use those dialects.

If you want to stick to American rules and just change the date format, go with

\DefineBibliographyExtras{english}{%
  \protected\def\mkbibdateshort#1#2#3{%
    \iffieldundef{#3}
      {}
      {\mkdayzeros{\thefield{#3}}%
       \iffieldundef{#2}{}{/}}%
    \iffieldundef{#2}
      {}
      {\mkmonthzeros{\thefield{#2}}%
       \iffieldundef{#1}{}{/}}%
    \iffieldbibstring{#1}
      {\bibstring{\thefield{#1}}}
      {\dateeraprintpre{#1}\mkyearzeros{\thefield{#1}}}}%
}

to load the British format for short dates.

If you also want to have the British long date format, you also need

  \protected\def\mkbibdatelong#1#2#3{%
    \iffieldundef{#3}
      {}
      {\mkbibordinal{\thefield{#3}}%
       \iffieldundef{#2}{}{\nobreakspace}}%
    \iffieldundef{#2}
      {}
      {\mkbibmonth{\thefield{#2}}%
       \iffieldundef{#1}{}{\space}}%
    \iffieldbibstring{#1}
      {\bibstring{\thefield{#1}}}
      {\dateeraprintpre{#1}\stripzeros{\thefield{#1}}}}%

in the \DefineBibliographyExtras{english}.

MWE

\documentclass{article}
\usepackage[backend=biber]{biblatex}


\DefineBibliographyExtras{english}{%
  \protected\def\mkbibdateshort#1#2#3{%
    \iffieldundef{#3}
      {}
      {\mkdayzeros{\thefield{#3}}%
       \iffieldundef{#2}{}{/}}%
    \iffieldundef{#2}
      {}
      {\mkmonthzeros{\thefield{#2}}%
       \iffieldundef{#1}{}{/}}%
    \iffieldbibstring{#1}
      {\bibstring{\thefield{#1}}}
      {\dateeraprintpre{#1}\mkyearzeros{\thefield{#1}}}}%
}

\begin{filecontents*}{\jobname.bib}
@misc{Latitude,
  author    = {Wikipedia},
  title     = {Latitude},
  url       = {https://en.wikipedia.org/wiki/Latitude},
  urldate   = {2015-04-09},
  date      = {2015-09},
}
@online{LatLonAlt,
  author      = {Dana, Peter H.},
  institution = {Department of Geography, University of Texas},
  title       = {Coordinate Systems Overview},
  url         = {http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html},
  urldate     = {2015-09-18},
  date        = {1999-12-15},
}
\end{filecontents*}

\addbibresource{\jobname.bib}
\nocite{*}

\begin{document}
\printbibliography
\end{document}