Используйте SpannableString установить подстрока жирным шрифтом.
String completeString = "<your complete string here>";
String subString = "<the substring you want in bold>";
SpannableString ss = new SpannableString(completeString);
ClickableSpan clickableSpan = new ClickableSpan() {
@Override
public void onClick(View textView) {
}
@Override
public void updateDrawState(TextPaint ds) {
super.updateDrawState(ds);
ds.setUnderlineText(false);
ds.setTypeface(Typeface.BOLD);
ds.setColor(<color that you want>);
}
};
if (completeString.indexOf(subString) > -1)
ss.setSpan(clickableSpan, completeString.indexOf(subString), completeString.indexOf(subString) + subString.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
textEdit.setText(ss, TextView.BufferType.SPANNABLE);