Hmm, my brand new Galaxy Tab 4 runs 8.1, but it doesn't have an entry for "advanced" under L&I, let alone "dictionary", darn it. Searching for it doesn't turn it up either.
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Elaine Pack
Sent from my phone/tablet. Please excuse any temporary top posting, brevity or tpyos. I AM an IT professional, but not necessarily in this hardware or software.
W/ my Moto G5+ (Oreo 8.1), the personal dictionary is quickest found under Settings > Type "Dictionary" (in top-most Search bar) > Personal Dictionary (as 1st option) > Personal Dictionary (toward bottom of screen > Choose language of dictionary > Edit to 1's heart's content 😀
Else, [ Settings > System > Languages & Input » Advanced > Personal Dictionary > Choose language ] is the long way.
As always, any long-press added words are here, too, but whatever can be added here — e.g., I often add alternative capitalizations of terms
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Elaine Pack
Charlotte NC
Sent from my phone. Please excuse any brevity or tpyos!