x <- c(
"Welcome to A I: the best W O R L D!",
"Hi I R is the B O M B for sure: we A G R E E indeed."
)
gsub("(?:(?=\\b(?:\\p{Lu}\\h+){2}\\p{Lu})|\\G(?!\\A))\\p{Lu}\\K\\h+(?=\\p{Lu})", "", x, perl=TRUE)
eCA8LSBjKAoJIldlbGNvbWUgdG8gQSBJOiB0aGUgYmVzdCBXIE8gUiBMIEQhIiwKCSJIaSBJIFIgaXMgdGhlIEIgTyBNIEIgZm9yIHN1cmU6IHdlIEEgRyBSIEUgRSBpbmRlZWQuIgopCmdzdWIoIig/Oig/PVxcYig/OlxccHtMdX1cXGgrKXsyfVxccHtMdX0pfFxcRyg/IVxcQSkpXFxwe0x1fVxcS1xcaCsoPz1cXHB7THV9KSIsICIiLCB4LCBwZXJsPVRSVUUp