# RevTex 4-2: Package babel Error: You haven't defined the language en yet

I am RevTex version 4-2 in combination with a Zotero-generated bib file. The bib file contains a lot of "random" entries in the "Language" field, such as "en", "eng", etc. These entries were automatically generated when adding the papers. RevTex 4-1 could deal with this bib file just fine. However, with RevTex 4-2, I get a lot of babel error messages related to the bibliography.

My question is: Is there any way to ignore the "Language" field in the bib file with RevTex 4-2, as it was apparently done in RevTex 4-1?

Note: I would like to avoid any solutions that require me to manually change > 1000 entries in my paper database to remove or correct the language entry.

Edit. Here is a minimal example:

\documentclass{revtex4-2}
\usepackage[english]{babel}
\begin{document}
\nocite{kubota_stress-induced_2012}
\nocite{kubota_stress-induced_2012_2}
% \bibliographystyle{apsrev4-1}
\bibliography{references}
\end{document}


Where references.bib reads

@article{kubota_stress-induced_2012,
title = {Stress-{Induced} {Perpendicular} {Magnetization} in {Epitaxial} {Iron} {Garnet} {Thin} {Films}},
volume = {5},
issn = {1882-0786},
url = {https://iopscience.iop.org/article/10.1143/APEX.5.103002/meta},
doi = {10.1143/APEX.5.103002},
language = {en},
number = {10},
urldate = {2019-09-07},
journal = {Applied Physics Express},
author = {Kubota, Masashi and Tsukazaki, Atsushi and Kagawa, Fumitaka and Shibuya, Keisuke and Tokunaga, Yusuke and Kawasaki, Masashi and Tokura, Yoshinori},
month = sep,
year = {2012},
pages = {103002}
}

@article{kubota_stress-induced_2012_2,
title = {Stress-{Induced} {Perpendicular} {Magnetization} in {Epitaxial} {Iron} {Garnet} {Thin} {Films}},
volume = {5},
issn = {1882-0786},
url = {https://iopscience.iop.org/article/10.1143/APEX.5.103002/meta},
doi = {10.1143/APEX.5.103002},
number = {10},
urldate = {2019-09-07},
journal = {Applied Physics Express},
author = {Kubota, Masashi and Tsukazaki, Atsushi and Kagawa, Fumitaka and Shibuya, Keisuke and Tokunaga, Yusuke and Kawasaki, Masashi and Tokura, Yoshinori},
month = sep,
year = {2012},
pages = {103002}
}


When I un-comment the bibliographystyle line, everything works fine. It seems that the new bibliographystyle changes the .bbl title entry from

\bibfield  {title}{\bibinfo {title} {Stress-{Induced} {Perpendicular} ...


to

\bibfield  {title}{{\selectlanguage {en}\bibinfo {title} {Stress-{Induced} {Perpendicular} ...


I guess one has to edit the bst file, or just use the old style.

• Have you asked zotero support how you can correct the wrong output of that software? Seems to be more an issue with zotero and not LaTeX ... Sep 16, 2019 at 16:11
• I understand this comment but given that RevTex 4-1 and many other classes seem to be fine with ignoring the Language field in bib files, I'd like to understand if that can also be achieved with RevTex 4-2. Frankly, I don't see a reason why the Language field should be evaluated. Sep 16, 2019 at 16:40
• Well, then please show us a short compilable tex code resulting in your issue. Please do not forget to add two used bib entries to your question ... Did you only change the documentclass or did you also change from BiBTeX to BibLaTeX/Biber? Sep 16, 2019 at 16:57

In Zotero, select Edit -> Preferences -> Better BibTeX -> Export and set Fields to omit from export to "language"
• Very useful! I had to play around a bit to make the better bibtex keys the same as the original zotero keys, to not break compatibility with my old documents. In case this is relevant for someone else, here is my citation key pattern: [auth:lower]_[Title:lower:select=1,1]_[year] Sep 17, 2020 at 8:06
• [zotero] gets you the original zotero key algorithm. Oct 12, 2020 at 11:39