"Legs Crossed" in Japanese (Terms On Chair vs. On Floor)

The term for "crossing [one's] legs" in Japanese is ashi-kumi 足組み. It's a noun formed from the phrase ashi wo kumu 足を組む, "to cross [one's] legs."

• isu ni suwatte ashi wo kumu
  椅子に座って足を組む
  To sit on a chair and cross [one's] legs.
• {kunda} ashi
  組んだ足
  Legs [that] {crossed}.
  Crossed legs.
  (body part qualified by relative clause in past form.)

Character: Nishikino Maki 西木野真姫
Anime: Love Live! School Idol Project (Episode 2, Stitch)

• On Floor
• Examples

On Floor

When crossing one's legs sitting on the floor, that is, to say "sitting Indian style" or "criss-cross applesauce" in Japanese, the term would be agura あぐら.

Character: Excel エクセル
Anime: Excel♥Saga, エクセル♥サーガ (Episode 4)

• Context: Excel pouts angrily.
• ude-gumi
  腕組み
  Arms crossed.
  • ~gumi is rendaku 連濁.

The lotus position in yoga, used as meditation pose in Buddhism, with feet soles facing up, also has its own term:

Character: Senjougahara Hitagi 戦場ヶ原ひたぎ
Anime: Koyomimonogatari 暦物語 (Episode 4, Stitch)

• kekkafuza
  結跏趺坐, or 結加趺坐
  Lotus position. (in yoga)
  Sitting with legs crosses, both soles facing up.
• hankafuza
  半跏趺坐
  A variant of the lotus position in which one doesn't cross their legs, just places one leg over the other.

Examples

For reference, some examples:

Character: Futaba Tae 双葉妙
Anime: Masamune-kun no Revenge, 政宗くんのリベンジ (Episode 11, Stitch)

• Context: a fujoshi 腐女子 sits on a chair with legs crossed.

Character: Sakurajima Mai 桜島麻衣
Anime: Seishun Buta Yarou wa Bunny Girl Senpai no Yume wo Minai, 青春ブタ野郎はバニーガール先輩の夢を見ない (Episode 1)

• Context: a bunny girl バニーガール sits with on a desk legs crossed

Character: Mizuchi Ayumi 海槌亜悠巳
Anime: Sukeban Deka スケバン刑事 (Episode 2, OVA)

• Context: a sukeban スケバン sits on a sofa with legs crossed.

Character: Sakamoto 坂本
Anime: Sakamoto Desu ga? 坂本ですが？ (Episode 1)

• Context: one cool dude sits on air with legs crossed.
• kuuki-isu
  空気椅子
  "Air chair." Keeping a pose as if you were sitting on a chair, without actually sitting on a chair, by just squatting very high.