\documentclass{report}
\usepackage{multicol}

\usepackage[utf8]{inputenc}
\usepackage[vietnam,english]{babel}
% test of use of vietnam.ldf for babel with utf8 input encoding; any 
% encoding that vietnam.sty supports can be used instead of utf8

\begin{document}
\selectlanguage{vietnam}
Test of lowercase letters:\\
áạàảãăắặằẳẵâấậầẩẫđéẹèẻẽêếệềểễíịìỉĩ\\
óọòỏõôốộồổỗơớợờởỡúụùủũưứựừửữýỵỳỷỹ

Test of uppercase letters:\\
ÁẠÀẢÃĂẮẶẰẲẴÂẤẬẦẨẪĐÉẸÈẺẼÊẾỆỀỂỄÍỊÌỈĨ\\
ÓỌÒỎÕÔỐỘỒỔỖƠỚỢỜỞỠÚỤÙỦŨƯỨỰỪỬỮÝỴỲỶỸ

Test whether \texttt{MakeLowercase} works correctly:\\
\MakeLowercase{%
ÁẠÀẢÃĂẮẶẰẲẴÂẤẬẦẨẪĐÉẸÈẺẼÊẾỆỀỂỄÍỊÌỈĨ\\
ÓỌÒỎÕÔỐỘỒỔỖƠỚỢỜỞỠÚỤÙỦŨƯỨỰỪỬỮÝỴỲỶỸ}

Test whether \texttt{MakeUppercase} works correctly:\\
\MakeUppercase{%
áạàảãăắặằẳẵâấậầẩẫđéẹèẻẽêếệềểễíịìỉĩ\\
óọòỏõôốộồổỗơớợờởỡúụùủũưứựừửữýỵỳỷỹ}

\input{vntest.tex}

\end{document}