\documentclass[12pt]{article}

\usepackage{fontspec}
\usepackage{polyglossia}

%\setlength{\textheight}{135mm}
\setlength{\textheight}{135mm}
%\setlength{\textheight}{100mm}

\usepackage{makeidx}
\makeindex

\setdefaultlanguage{english}
\setromanfont{Noto Serif}
\setmainfont{Noto Serif}

\newfontfamily\hindifont{Noto Serif Devanagari}[Script=Devanagari]
\setotherlanguage{hindi}
\newfontfamily\bengalifont{Noto Serif Bengali}[Script=Bengali]
\setotherlanguage{bengali}
\newfontfamily\punjabifont{Noto Serif Gurmukhi}[Script=Gurmukhi]
\setotherlanguage{punjabi}
%\newfontfamily\gujaratifont{Noto Serif Gujarati}[Script=Gujarati]
%\setotherlanguage{gujarati}
\newfontfamily\tamilfont{Noto Serif Tamil}[Script=Tamil]
\setotherlanguage{tamil}
\newfontfamily\kannadafont{Noto Serif Kannada}[Script=Kannada]
\setotherlanguage{kannada}
\newfontfamily\telugufont{Noto Serif Telugu}[Script=Telugu]
\setotherlanguage{telugu}
\newfontfamily\odiafont{Noto Sans Oriya}[Script=Odia]
\setotherlanguage{odia}
\newfontfamily\malayalamfont{Noto Serif Malayalam}[Script=Malayalam]
\setotherlanguage{malayalam}
%\newfontfamily\sinhalafont{Noto Serif Sinhala}[Script=Sinhala]
%\setotherlanguage{sinhala}
\newfontfamily\thaifont{Noto Serif Thai}[Script=Thai]
\setotherlanguage{thai}
\newfontfamily\laofont{Noto Serif Lao}[Script=Lao]
\setotherlanguage{lao}

\newcommand{\EN}[1]{\textenglish{#1}}

\pagestyle{empty}
\begin{document}
\thispagestyle{empty}

\begin{hindi}

हिंदी\index{हिंदी \EN{(Hindi, Devanagari)}}
मराठी\index{मराठी \EN{(Marathi, Devanagari)}}
नेपाली\index{नेपाली \EN{(Nepali, Devanagari)}}

\end{hindi}

\begin{bengali}

বাংলা\index{বাংলা \EN{(Bengali)}}
অসমীয়া\index{অসমীয়া \EN{(Assamese, Bengali)}}

\end{bengali}

\begin{punjabi}

ਪੰਜਾਬੀ\index{ਪੰਜਾਬੀ \EN{(Punjabi, Gurmukhi)}}

\end{punjabi}

\begin{odia}

ଓଡ଼ିଆ\index{ଓଡ଼ିଆ \EN{(Oriya)}}

\end{odia}

\begin{tamil}

தமிழ்\index{தமிழ் \EN{(Tamil)}}

\end{tamil}

\begin{telugu}

తెలుగు\index{తెలుగు \EN{(Telugu)}}

\end{telugu}

\begin{telugu}

తెలుగు\index{తెలుగు \EN{(Telugu)}}

\end{telugu}

\begin{kannada}

ಕನ್ನಡ\index{ಕನ್ನಡ \EN{(Kannada)}}

\end{kannada}

\begin{malayalam}

മലയാളം\index{മലയാളം \EN{(Malayalam)}}

\end{malayalam}

%\begin{sinhala}
%
%සිංහල\index{සිංහල \EN{(Sinhala)}}
%
%\end{sinhala}

\begin{thai}

ภาษาไทย\index{ภาษาไทย \EN{(Thai)}}

\end{thai}

\begin{lao}

ພາສາລາວ\index{ພາສາລາວ \EN{(Lao)}}

\end{lao}


\printindex

\end{document}