FAQ

I really want to use polyglossia

Set your document language and fonts up like this:

\usepackage{polyglossia}
\usepackage[style=american]{csquotes}
\setmainlanguage[variant=american]{english}
\setotherlanguage[variant=ancient]{greek}
\setotherlanguage{hebrew}

\newfontfamily\greekfont{SBL BibLit}[Ligatures=TeX,Script=Greek,Contextuals=Alternate]
\newfontfamily\hebrewfont{SBL BibLit}[Ligatures=TeX,Script=Hebrew,Contextuals=Alternate,Scale=1.2]

\usepackage[style=sbl]{biblatex}

\DefineBibliographyExtras{english}{%
  \uspunctuation
  \protected\def\mkdaterangecomp{%
    \mkdaterangetrunc{long}}%
  \protected\def\mkdaterangeterse{%
    \mkdaterangetrunc{short}}%
  \protected\def\mkdaterangecompextra{%
    \mkdaterangetruncextra{long}}%
  \protected\def\mkdaterangeterseextra{%
    \mkdaterangetruncextra{short}}%
  \protected\def\mkbibdatelong#1#2#3{%
    \iffieldundef{#3}
      {}
      {\thefield{#3}%
       \iffieldundef{#2}{}{\nobreakspace}}%
    \iffieldundef{#2}
      {}
      {\mkbibmonth{\thefield{#2}}%
       \iffieldundef{#1}{}{\space}}%
    \iffieldbibstring{#1}
      {\bibstring{\thefield{#1}}}
      {\dateeraprintpre{#1}\stripzeros{\thefield{#1}}}}%
}

I'm using Australian English and Oxford commas are not printed

By default biblatex does not use Oxford commas for languages other than American English. Add this to your preamble (assuming you are using babel):

\DefineBibliographyExtras{australian}{%
  \def\finalandcomma{\addcomma}%
}