I think that's what we call the Japanese accent. If you speak/write English as you would do Japanese in some way or another, your English is 日本語訛りの英語 and vice versa. It may not be as common to call it a foreign accent if it's writing. But it is a quintessential example of foreign accent as a result of influence from your native language.
I tend to doubt that L vs. R is so special in this regard it deserves its own term in a colloquial everyday language. I never heard of such a specialized term myself, although accent trainers, linguists specializing in L2 acquisition, and other professionals might have come up with one. But if they did, I still highly doubt it became part of the Japanese vernacular.
FWIW, I'm a native Japanese speaker who is interested in human language and language learning in general, and have never heard my fellow countrymen use such a specialized term that only refers to one specific aspect of the typical Japanese accent that only manifests when we speak one particular foreign language called English. If anything, it's quite rare for your average Japanese guy on the street to talk about a foreign language in the first place.
Would the word "日本語訛り" be too general of a term for your purpose?