即使首先加载了 babel，datetime 也会导致日期格式不正确

Question 1

该文件dt-welsh.def似乎有问题，因为它确实

\DeclareRobustCommand*\datewelsh{%
\renewcommand{\formatdate}[3]{%
\@day=##1\relax\@month=##2\relax\@year=##3\relax
\ifnum\@day=1\relax 1\/$^{\mathrm{a\tilde{n}}}$\else
\number\@day\fi \space a\space viz\space
\monthnamewelsh[\@month]\space\number\@year}}%

如果我\datewelsh在文档中重新定义，如以下示例所示

\documentclass{article}
\usepackage[welsh]{babel}
\usepackage{datetime}

\makeatletter
\DeclareRobustCommand*\datewelsh{%
\renewcommand{\formatdate}[3]{%
\@day=##1\relax\@month=##2\relax\@year=##3\relax
\ifnum\@day=1\relax 1\/$^{\mathrm{a\tilde{n}}}$\else
\number\@day\fi \space %a\space viz\space
\monthnamewelsh[\@month]\space\number\@year}}%
\makeatother

\begin{document}
\day=0
\loop\ifnum\day<10
  \advance\day by 1
  \today\endgraf
\repeat

\end{document}

我明白了

在此处输入图片描述

不知道威尔士的日期应该如何出现，这是我能做的最好的。

“a viz”部分似乎来自布列塔尼语（参见dt-breton.def）。

Answer

该文件dt-welsh.def似乎有问题，因为它确实

\DeclareRobustCommand*\datewelsh{%
\renewcommand{\formatdate}[3]{%
\@day=##1\relax\@month=##2\relax\@year=##3\relax
\ifnum\@day=1\relax 1\/$^{\mathrm{a\tilde{n}}}$\else
\number\@day\fi \space a\space viz\space
\monthnamewelsh[\@month]\space\number\@year}}%

如果我\datewelsh在文档中重新定义，如以下示例所示

\documentclass{article}
\usepackage[welsh]{babel}
\usepackage{datetime}

\makeatletter
\DeclareRobustCommand*\datewelsh{%
\renewcommand{\formatdate}[3]{%
\@day=##1\relax\@month=##2\relax\@year=##3\relax
\ifnum\@day=1\relax 1\/$^{\mathrm{a\tilde{n}}}$\else
\number\@day\fi \space %a\space viz\space
\monthnamewelsh[\@month]\space\number\@year}}%
\makeatother

\begin{document}
\day=0
\loop\ifnum\day<10
  \advance\day by 1
  \today\endgraf
\repeat

\end{document}

我明白了

在此处输入图片描述

不知道威尔士的日期应该如何出现，这是我能做的最好的。

“a viz”部分似乎来自布列塔尼语（参见dt-breton.def）。

Question 2

编辑：要修复先前出现的虚假间距问题，请将中的文件名称更改\ProvidesFile为dt-welsh.def，并重命名文件本身（egreg 对我这个问题的回答)：

dt-welsh.def这是基于的修复版本egreg 的回答，egreg 的评论gloss-welsh.ldf以及从新版本更新的polyglossia。

许可证不允许我发布修改后的版本dt-welsh.def，我无法找到一种干净的方式来加载不同名称的文件。因此，它被命名dt-cymraeg.def为但仅当重命名为时才有效dt-welsh.def。它不能以该形式分发，但可以在您自己的系统上以该形式使用。

希望datetime最终能修复，以便更接近于生成正确的输出，而无需这样做。当然，该软件包已更新为不包含a viz，这是件好事。当前的错误是从中复制而来的babel，我相信作者知道这些错误。也许这会通过为威尔士语提供正确的模式有所帮助。

%% dt-cymraeg.def
%% Additions and changes are copyright 2015 Clea F. Rees
%% Code from dt-welsh.def copyright 2015 Nicola Talbot (see below)
%% Code from gloss-welsh.ldf copyright 2008-2010 François Charette,
%% 2013 Élie Roux, 2011-2015 Arthur Reutenauer
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3
% of this license or (at your option) any later version.
% The latest version of this license is in
%   http://www.latex-project.org/lppl.txt
% and version 1.3 or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
%
% This work has the LPPL maintenance status `maintained'.
%
% The Current Maintainer of this work is Clea F. Rees.
%
% This work consists of the file dt-cymraeg.def
%
% The file dt-cymraeg.def is a derived work under the terms of the
% LPPL. It is based on dt-welsh.def which is part of the datetime
% package by Nicola Talbot. A copy of datetime, including the
% unmodified version of dt-welsh.def is available from
% http://tug.ctan.org/cgi-bin/ctanPackageInformation.py?id=datetime.
%
% The modifications are also derivative under the terms of the LPPL. They
% are based on code modified from gloss-welsh.ldf which is part of
% polyglossia 2015/08/06 v1.42.0 by François Charette, Élie Roux
% and Arthur Reutenauer. A copy of polyglossia, including gloss-welsh.ldf
% is available
% from http://tug.ctan.org/cgi-bin/ctanPackageInformation.py?id=polyglossia.
%%
\ProvidesFile{dt-cymraeg.def}[$Id: dt-cymraeg.def 3789 2015-08-31 02:01:23Z cfrees $]
\providecommand*\dt@cymraeg@neges{%
  \PackageWarning{dt-cymraeg.def}{This is a MODIFIED version of dt-welsh.def. Breakage should under no circumstances be blamed on the author of the original file.}}
\dt@cymraeg@neges
\renewcommand*\dt@cymraeg@neges{\relax}
\providecommand*\ordinaldatewelsh[1]{%
  #1\ifcase#1\relax%
  \or\textsuperscript{af}%
  \or\textsuperscript{ail}%
  \or\textsuperscript{ydd}%
  \or\textsuperscript{ydd}%
  \or\textsuperscript{ed}%
  \or\textsuperscript{ed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \else\textsuperscript{ain}\fi}%
\global\let\ordinaldatewelsh\ordinaldatewelsh
\providecommand\dayofweeknameidwelsh[1]{%
dydd\space%
\ifcase#1\relax
\or Sul%
\or Llun%
\or Mawrth%
\or Mercher%
\or Iau%
\or Gwener%
\or Sadwrn%
\fi}%
\global\let\dayofweeknameidwelsh\dayofweeknameidwelsh
\providecommand{\shortdayofweeknameidwelsh}[1]{%
\ifcase#1\relax%
\or Sul%
\or Llun%
\or Maw.%
\or Mer.%
\or Iau%
\or Gwen.%
\or Sad.%
\fi}%
\global\let\shortdayofweeknameidwelsh\shortdayofweeknameidwelsh
\providecommand{\monthnamewelsh}[1][\month]{%
\@orgargctr=#1\relax%
\ifcase\@orgargctr%
\PackageError{datetime}{Invalid Month number \the\@orgargctr}{%
Month numbers should go from 1 to 12}%
\or Ionawr%
\or Chwefror%
\or Mawrth%
\or Ebrill%
\or Mai%
\or Mehefin%
\or Gorffennaf%
\or Awst%
\or Medi%
\or Hydref%
\or Tachwedd%
\or Rhagfyr%
\else%
\PackageError{datetime}{Invalid Month number \the\@orgargctr}{%
Month numbers should go from 1 to 12}%
\fi}%
\global\let\monthnamewelsh\monthnamewelsh
\DeclareRobustCommand*\datewelsh{%
\renewcommand{\formatdate}[3]{%
  \@day=##1\relax\@month=##2\relax\@year=##3\relax
  \number\@day%
  \ifcase\@day\relax%
  \or\textsuperscript{af}%
  \or\textsuperscript{ail}%
  \or\textsuperscript{ydd}%
  \or\textsuperscript{ydd}%
  \or\textsuperscript{ed}%
  \or\textsuperscript{ed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \or\textsuperscript{eg}%
  \or\textsuperscript{fed}%
  \else\textsuperscript{ain}%
  \fi%
  \space%
  \monthnamewelsh[\@month]\space\number\@year}%
}%
\global\let\datewelsh\datewelsh
\providecommand{\shortmonthnamewelsh}[1][\month]{%
\@orgargctr=#1\relax%
\ifcase\@orgargctr%
\PackageError{datetime}{Invalid Month number \the\@orgargctr}{%
Month numbers should go from 1 (jan.) to 12 (dec.)}% rhai o Yale ond 'dw i ddim yn cytuno â'i rhai Saesneg chwaith! (efaillai bod nhw'n safonol a ffurfiol?)
\or Ion.%
\or Chwe.% Chwef. yn ôl Yale??!!
\or Maw.%
\or Ebr.%
\or Mai%
\or Meh.%
\or Gorff.%
\or Awst.%
\or Medi%
\or Hyd.%
\or Tach.%
\or Rhag.%
\else%
\PackageError{datetime}{Invalid Month number \the\@orgargctr}{%
Month numbers should go from 1 (jan.) to 12 (dec.)}%
\fi}
\endinput
%%
%% End of file dt-cymraeg.def.

如果您想使用此版本，请将内容复制到系统上的文件中。将文件另存为dt-welsh.def并将其放在您的个人 TEXMF 树或工作目录中。请注意不要在未重命名文件的情况下重新分发。那么一切就都应该正常了。再提醒一下，您使用的是一个修改版本，因此它不会从软件包的任何更新或错误修复中受益。

尤其，在没有确认你可以产生错误之前，不要向datetime作者报告错误 没有 您的 TEXMF 树中的此文件。

据我所知，这可以正确获取标准日期格式以及长格式和短格式：

Answer