Biblatex (biblatex-apa style) customization: nodate bibstring and ampersand

Question

I'm trying to set up my bibliography with Biblatex, styled with biblatex-apa. My document is in Spanish language. So I set up the package in the preamble as follows:

\usepackage[babel, spanish=quotes]{csquotes}
\usepackage[backend=biber, style=apa,sortlocale=auto]{biblatex}
\DeclareLanguageMapping{spanish}{spanish-apa}

Citations inside the text works as desired. But \printbibliography produces following output:

That ampersand in the first citation should be a "y". And the nodate string should be "sin fecha". The weird thing is that neither in spanish-apa.lbx or american-apa.lbx is defined the bibstring nodate. Anyway, adding to the spanish-apa.lbx the obvious:

\NewBibliographyString{nodate}

%into the \DeclareBibliographyStrings{ 
nodate           = {{sin\space fecha}{{}s\adddot f\adddot}},

Does not make any difference.

I've prepared a MWE, tested online in writeLatex, to debug the nodate issue. Changing english to spanish, both in babel and in DeclareLanguageMapping, reproduce the issue.

\documentclass[endnotes]{apa6e}
\usepackage[english]{babel}
\usepackage{csquotes} 
\usepackage[style=apa]{biblatex} 
\DeclareLanguageMapping{english}{english-apa}
\usepackage[T1]{fontenc}
\title{A title}
\author{An Author}
\shorttitle{A title}
\authornote{}
\abstract{An abstract}

\begin{filecontents}{apa-test-bib1.bib}
@book{Saussure1995,
Author = {Ferdinand de Saussure},
Origyear = {1916},
Publisher = {Payot},
Title = {Cours de Linguistique G{\'e}n{\'e}rale},
Year = {1995}}

@book{Labov1972,
Address = {Philadelphia},
Author = {William Labov},
Publisher = {University of Pennsylvania Press},
Title = {Sociolinguistic Patterns},
}

\end{filecontents}
\addbibresource{apa-test-bib1.bib}

\begin{document}

This is some text. \cite{Saussure1995,Labov1972}
\printbibliography
\end{document}

Answer 1

Long dates for Spanish are not implemented in biblatex-apa [Update: now they are; see below]. The following example modifies the appropriate definitions first appearing in spanish-apa.lbx to workaround a bug in the package which made the nodate label to appear instead of the actual localised string. It makes the Oxford comma to go away, the ampersand to be translated, the nodate appear as "sin fecha" and long dates to appear correctly in citations and references. It cites works twice to show the et al feature.

\documentclass{article}
\usepackage{polyglossia}
\setdefaultlanguage{spanish}
\usepackage{csquotes}
\usepackage{shortvrb}
\usepackage{fontspec}
% Biblatex-APA
\usepackage[backend=biber,style=apa]{biblatex}
\DeclareLanguageMapping{spanish}{spanish-apa}

\DefineBibliographyStrings{spanish}{%
nodate = {sin fecha}
}

\AtBeginDocument{\renewcommand*{\finalandcomma}{}}

% Evitar ampersand en referencias con varios autores. CITAS
\AtEveryCitekey{\renewcommand*{\finalnamedelim}{%
    \ifthenelse{\value{listcount}>\maxprtauth}
      {}
      {\ifthenelse{\value{liststop}>2}
         {\finalandcomma\addspace\bibstring{and}\space}
         {\addspace\bibstring{and}\space}}}}

% Evitar ampersand en referencias con varios autores. REFERENCIAS
\AtBeginBibliography{%
\renewcommand*{\finalnamedelim}{%
    \ifthenelse{\value{listcount}>\maxprtauth}
      {}
      {\ifthenelse{\value{liststop}>2}
         {\finalandcomma\addspace\bibstring{and}\space}
         {\addspace\bibstring{and}\space}}}
  \protected\def\mkbibdateapalongextra#1#2#3{%   %%% #1 #2 #3 = año mes día
    \iffieldundef{#1}%                           %%% ¿definido el año?
      {}%
      {\iffieldbibstring{#1}{\biblcstring{\thefield{#1}}}{\thefield{#1}}\printfield{extrayear}}%
    \iffieldundef{#2}%                           %%% mes?
      {}%
      {\iffieldundef{#1}%                        %%% ¿definido el año?
        {}%
        {\addcomma\addspace}%                    %%% , [día]
    \iffieldundef{#3}%                           %%% ¿definido el día?
      {}%
      {\ifthenelse{\iffieldundef{#2}\OR\iffieldundef{#1}}% %falta mes o año
        {}%
        {\stripzeros{\thefield{#3}}\addspace de\addspace}}%    % <día> "de"
       \mkbibmonth{\thefield{#2}}%              %%% <mes>
  }}%                
  \protected\def\mkbibdateapalongmdy#1#2#3{%   %%% #1 #2 #3 = año mes día
    \iffieldundef{#3}%                         %%% ¿definido el día?
      {}%
      {el\addspace\stripzeros{\thefield{#3}}}% %%% HAY DÍA.  el [día]
    \iffieldundef{#2}%                         %%% ¿definido el mes?
      {\addspace{en}\addspace}%                %%% NO HAY MES. en [año]
      {\iffieldundef{#3}%                      %%% ¿definido el día?
        {en\addspace}%                         %%% NO HAY DÍA. en [mes]
        {\addspace{de}\addspace}%              %%% HAY DÍA Y MES. [día] de [mes]
       \mkbibmonth{\thefield{#2}}{\addspace{de}\addspace}}% %%% [mes] de [año]
    \iffieldundef{#1}%                         %%% ¿definido el año?
      {}%
      {\iffieldundef{#2}%                      %%% ¿definido el mes?
        {}%
        {\addspace}%                           %%% HAY AÑO Y MES.
       \thefield{#1}}}}%                       %%% año.  

\begin{filecontents}{apa-minimal.bib}
@ONLINE{paconet1,
    TITLE = {Referencia online; fecha de URL con año, mes y día},
    URL = {http://paconet.org},
    ORGANIZATION = {Paconet Corporation},
    URLDATE = {2001-09-15},
    DATE = {2001-09-15},
}
@BOOK{varios5,
  AUTHOR = {Benito Botín and Carlos Cabrero and Damián Domínguez and Ernesto Enríquez and Fernando Fernández},
  TITLE = {Un libro sin fecha y con cinco autores},
}
\end{filecontents}

\addbibresource{apa-minimal.bib}

\begin{document}
\textcite{paconet1,varios5}

\textcite{paconet1,varios5}

\printbibliography
\end{document}