gistfile1.txt

FreeTypeFontGenerator generator = new FreeTypeFontGenerator(Gdx.files.internal("data/arial.ttf"));
FreeTypeFontParameter parameter = new FreeTypeFontParameter();
parameter.size = 32;

FreeTypeBitmapFontData fontData = generator.generateData(parameter);
BitmapFont font = generator.generateFont(parameter);
generator.dispose();

Skin skin = new Skin(new TextureAtlas(Gdx.files.internal("data/uiskin.atlas")));
skin.add("ft-font", font, BitmapFont.class);		
skin.load(Gdx.files.internal("data/uiskin.json"));

Update your uiskin.json styles to use ft-font in lieu of default-font.