Using OTF font for Arabic/Persian text results following warning without any visible text...
...
Warning: distance-field glyph is not available with index 1575
Warning: distance-field glyph is not available with index 1688
Warning: distance-field glyph is not available with index 1608
Warning: distance-field glyph is not available with index 1604
Warning: distance-field glyph is not available with index 1587
Warning: distance-field glyph is not available with index 1575
Warning: distance-field glyph is not available with index 1582
Warning: distance-field glyph is not available with index 1578
...

Text {
            id: txt
            //text: "some text" //Works!
            text: "some text مرگ بر آمریکا" //Not works!
            verticalAlignment: Text.AlignVCenter
            font {
                family: "Adobe Arabic"
                pixelSize: 16
            }
}

More info about font:
Adobe Arabic - version 2.006 - OpenType Layout - PostScript Outlines -> Failed!
BBCNassim - version 1.051 - OpenType Layout - PostScript Outlines -> Failed!
BBCNassim - version 1.051 - OpenType Layout - TrueType Outlines -> SUCCESS!