Type "about:config" in your browser to access your "Opera" options page. This page lists your available languages and fonts. Remember, not all fonts are installed and you are possibly using the default fonts only.
Locate the option "Use Bitmap Fonts for Complex Scripts" and check the box that says "Yes" next to the option. This will enable your uninstalled fonts to be used with the "Opera" browser with your preferred language settings. Click "Save" to apply the changes.
Search your "Download" folder for your downloaded fonts. Open the folder and choose the fonts you wish to install. From the "File" menu, choose "Extract All" for each font. This will unzip the folder they are contained in.
Select "Browse" from the pop-up window and locate your "Opera" browser folder. Open the folder for your browser and select "Opera Fonts." Press "Okay" to open transfer your fonts to your browser.