Script on shirt is in Dova (Dragon language) and translates to:
By his honor is sworn,
To keep evil forever at bay,
And the fiercest foes rout,
When they hear triumph’s shout,
Dragonborn for your blessing we pray.
And the scrolls have foretold,
Of black wings in the cold,
That when brothers wage war come unfurled,
Alduin, bane of kings,
Ancient shadow unbound,
With a hunger to swallow the world."