The story
From the mispronunciation of the word English common to Japanese speakers, who have difficulty distinguishing /l/ ~ /r/ sounds. The Japanese transliteration of the word English, イングリッシュ (Ingurisshu) is often used for teaching purposes. In that word, /ɾ/ (romanized as r) is pronounced instead of the English /l/.
Etymology from Wiktionary, CC BY-SA 4.0.