书目字符串‘letterto’未定义

Question

我正在使用 biblatex 和历史风格，一切都运行顺利，直到我尝试了@letter条目类型。我还重新定义了\smartcite宏，让脚注看起来更符合我的喜好。

以下是 MWE：

\documentclass{article}  
\usepackage{filecontents}
\usepackage{csquotes}
\usepackage[backend=biber,style=historian,autocite=footnote]{biblatex}

\begin{filecontents}{literature.bib}
@letter{saganA,
    author = {Sagan, Naomi},
    namec = {Greenpeace},
    Year = {24 February, 1990},
}
\end{filecontents}

\bibliography{literature.bib}

%% redefine the \smartcite macro so that it does not add parentheses in footnotes
%% see http://tex.stackexchange.com/questions/68175/biblatex-autocite-in-case-of-would-be-nested-footnotes
\DeclareCiteCommand{\smartcite}[\iffootnote\textnormal\mkbibfootnote]
  {\usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}}
  {\multicitedelim}
  {\usebibmacro{postnote}}

\DeclareMultiCiteCommand{\smartcites}
    [\iffootnote\textnormal\mkbibfootnote]{\smartcite}{\multicitedelim}

\AtEveryBibitem{
  \clearlist{address}
  \clearlist{location}
}

\begin{document}  
This is a test.\autocites{saganA}
\end{document}  

我收到警告：

Package biblatex Warning: Bibliography string 'letterto' undefined
(biblatex)                at entry 'saganA' on input line 35.

（其中 35 是最后一行“\end{document\”）

输出如下：

我怎样才能替换“致函“用“致”字母”（不加粗，带有空格）还是去掉它？

Answer 1

包括

\DefineBibliographyStrings{english}{
  letterto = {letter to}
}

提供letterto biblatex 字符串的替换。