Biblatex, apa-style, polyglossia and multilingual-bibliography

Question

For my scientific article I need to use some sources that are in Korean, which is why I've switched from using pdflatex\bibtex to xelatex and biber.

I've managed to get biblatex with apa style working (through other posts on this site). But I've encountered several problems so far and I am not sure whats causing them. I am facing the following four problems now:

1. The bibliography is not sorted (even though I used sorting=nyt).
2. If there is more than one source from one year, biblatex automatically adds an sorting system (by adding an a, b, c and so on), how can I disable this?
3. The issue of the journal is not displayed in the bibliography.
4. The text is not adjusted correctly, as can be seen in the pdf.

My MWE:

\documentclass[a4paper,12pt]{article}
\usepackage{polyglossia}
\usepackage{csquotes}
\usepackage[backend=biber,style=apa,sorting=nyt]{biblatex}
\DeclareLanguageMapping{american}{american-apa}
\DefineBibliographyExtras{english}{%
  \protected\def\mkbibdateapalong#1#2#3{%
    \iffieldundef{#1}%
      {}%
      {\thefield{#1}}%
    \iffieldundef{#2}%
      {}%
      {\iffieldundef{#1}%
        {}%
        {\addcomma\addspace}%
       \mkbibmonth{\thefield{#2}}}%
    \iffieldundef{#3}%
      {}%
      {\ifthenelse{\iffieldundef{#2}\OR\iffieldundef{#1}}%
        {}%
        {\addspace}%
       \stripzeros{\thefield{#3}}}}%
  \protected\def\mkbibdateapalongextra#1#2#3{%
    \iffieldundef{#1}%
      {}%
      {\thefield{#1}\printfield{extrayear}}%
    \iffieldundef{#2}%
      {}%
      {\iffieldundef{#1}%
        {}%
        {\addcomma\addspace}%
       \mkbibmonth{\thefield{#2}}}%
    \iffieldundef{#3}%
      {}%
      {\ifthenelse{\iffieldundef{#2}\OR\iffieldundef{#1}}%
        {}%
        {\addspace}%
       \stripzeros{\thefield{#3}}}}%
  \protected\def\mkbibdateapalongdmy#1#2#3{%
    \iffieldundef{#3}%
      {}%
      {\stripzeros{\thefield{#3}}}%
    \iffieldundef{#2}%
      {}%
      {\iffieldundef{#3}%
        {}%
        {\addspace}%
       \mkbibmonth{\thefield{#2}}}%
    \iffieldundef{#1}%
      {}%
      {\ifthenelse{\iffieldundef{#2}\OR\iffieldundef{#3}}%
        {}%
        {\addspace}%
       \thefield{#1}}}}
\addbibresource{BT.bib}
\usepackage{fontspec}
\usepackage{xeCJK}                      % package for Korean fonts
\setmainlanguage[variant=american]{english}
\setCJKmainfont{Dotum}              % For Korean font
\setmainfont{Times New Roman}           % Standard font
\begin{document}
\section{Introduction}
Three main things when talking about IPO research: underpricing, long-term overpricing and IPO waves \parencite{Ka91}.
This is a test \parencite{Ro86,TiTr86, Ch99, Ch11}.

\printbibliography[title=Bibliography]
\end{document}

Here my .bib file:

@article{Ro86,
author = {K. Rock},
title = {Why new issues are underpriced},
journaltitle = {Journal of Financial Economics},
volume = {15},
year = {1986},
pages = {187-212}
}
@article{TiTr86,
author = {S. Titman and B. Trueman},
title = {Information Quality and the Valuation of New Issues},
journaltitle = {Journal of Accounting and Economics},
volume = {8},
year = {1986},
pages = {159-172}
}
@article{Ch99,
author = {M.-S. Choi},
title = {A Study on Initial Returns and Underpricing of {IPOs}},
journaltitle = {The Korean Journal of Finance},
volume = {12},
year = {1999},
pages = {197-226},
origlanguage = {Korean},
origtitle = {신규공모주의 공모가격 할인과 초기성과에 대한 연구},
origpublisher = {재무연구}
}
@article{Ch11,
author = {M.-S. Choi},
title = {Review of Empirical Studies on {IPO} Activity and Pricing Behavior in Korea},
journaltitle = {Asian Review of Financial Research},
volume = {24},
issue ={2},
year = {2011},
pages = {621-663},
}
@article{Ka91,
author = {H. S. Kang},
title = {An Empirical Study on the Effect of the Activities of Investment banks on IPO Pricing},
journaltitle = {The Korean Journal of Financial Management},
volume = {8},
issue = {2},
year = {1991},
pages = {31-45},
origlanguage = {Korean},
origtitle = {투자은행이 IPO의 가격형성에 미치는 영향에 관한 실증분석},
origpublisher = {재무관리연구}
}

Answer 1

With regard to question 3 (issue of journal not displayed), I quote section 2.2.2 (Data Fields) of the biblatex manual:

issue

field (literal)

The issue of a journal. This field is intended for journals whose individual issues are identified by a designation such as ‘Spring’ or ‘Summer’ rather than the month or a number. Since the placement of issue is similar to month and number, this field may also be useful with double issues and other special cases.

[...]

number

field (literal)

The number of a journal or the volume/number of a book in a series.

Looking at your .bib file, I strongly suspect that you should replace your issue fields with number fields (which are displayed correctly by biblatex-apa).