I'm using biblatex with the historian style, and everything's been working smoothly until I tried the @letter entry type. I'm also redefining the \smartcite macro to get the footnotes to look more like I prefer.
Here's a 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}
I'm getting a warning:
Package biblatex Warning: Bibliography string 'letterto' undefined
(biblatex) at entry 'saganA' on input line 35.
(where 35 is the last line "\end{document\")
And the output looks like this:

How can I replace "letterto" with "letter to" (not bold, with blank space) or get rid of it?