In your Jasper Environment "IReport"
If you want to generate a PDF report for example
Its better to choose (Preview -> PDF Preview) from your ireport app
NOT default value (Internal Preview)
Text fields properties
For Text fields you should to assign some properties
1. Font name : a font that support your locale "Farsi"
2. Pdf font name : a font that support your locale "Farsi"
3. Pdf Embeded : true
4. Pdf Encoding : depend on your language "Farsi" -> "Identity-H (Unicode with horizontal writing)"
Note
If you does NOT install a font that support your language "Farsi"
Its so easy
Just get your favorite font "....ttf"
Then from ireport
(Tools -> Options -> Fonts tab -> Install Font button -> .... )