List of various terms of endearment that can be used in different languages. A lot of them are gender neutral. Now in alphabetical order.
Habibi ŰŰšÙŰšÙ (m) (my love)
Habibti ŰŰšÙŰšŰȘÙ (f) (my love)
Ya hayati Ùۧ ŰÙۧŰȘÙ (my life)
Ya qalbi Ùۧ ÙÙŰšÙ (my heart)
Ya ruhi Ùۧ ۱ÙŰÙ (my soul)
Hubbi/hobbi ŰŰšÙ (my love)
Estimat (m) /estimada (f) (dear)
Amor/amor meu (love/my love)
Sol (sun) (used more like "és un sol" ('they're a sun'??) and normally used when talking about well-behaved children lmao.
"Reiet meu" could also be used (means 'my little king') (m)
"Carinyo" (from spanish Cariño i guess)
"Bonic (m)/bonica (f)" (means nice or pretty (physically)) ("bonica" in feminine is more common as a term of endearment)
Vida (life) (can also be "videta" (diminutive version))
BombĂł (that's like a chocolate sweet lmao)(used normally with women)
Princesa (means princess) (f)
Zlato (gold, my precious)
MilĂĄÄku (dearest, little dear)
Smukke (pretty/beautiful)
Elskede/elskling (beloved)
KĂŠreste (dearest and also used for the term girlfriend/boyfriend)
Snut (sorta like babe, a bit outdated)
Smuksak (beautiful but only for endearment)
Pusling (Pus in diminutive)
Musling (mouse diminutive)
Putte[animal] (cuddle[animal of choice], most used is: animal, mouse and pig, but other animals or objects happen)
AllerkĂŠreste (most loved, argumentative)
Basse (cute fat, might come from bear, mostly used for children and men)
Azizam ŰčŰČÛŰČÙ
 (my dear)
Asalam ŰčŰłÙÙ
(my honey)
Filipino (from various local languages, all gender neutral)
Mahal, sinta (tagalog) (love)
alternatively add "ko" or "aking" to turn it into "my love" (e.g. mahal ko, sinta ko; aking mahal, aking sinta) with "aking" being used more often when talking about the one you love to a 3rd party;
or turn it into a verb (e.g. aking minamahal, kasintahan) to make it "lover"
Paraluman, irog, liyag, giliw (tagalog) (darling) these are older terms though, you won't hear or see them being used unless you're lovers with someone đExtrađ
Tangi (tagalog) (only one)
Tinatangi (tagalog) (the one i hold dear/the only one for me)
Tinadhana - fated (from the root word "tadhana" meaning fate, which in and of itself should also be a term of endearment and I stand by that)
Hinigugma (bisaya) (beloved) (very old)
Palangga/pangga/langga or "ga" for short and sometimes pagingging (ilonggo) (love) (can also be used platonically or between family members)
Kalasahan (tausug) (beloved) (this is pronounced with an emphasis in the SA syllable (as in kalaSAhan) instead of the LA like in the tagalog word LAsa (which means taste)
Jowa (filipino slang) (significant other/boyfriend/girlfriend)
Bebe, bebe ko, beh, bhe, bhie, bih (filipino slang) (babe)
Lablabs (filipino slang) (literally "love-love" in a heavy filipino accent)
Armaani (my darling (A bit old fashioned to say.))
Höpönassu/höpönassukka/höpsö (silly)
Kalleimpani (my most valued one)
Kulta/kultaseni/kultu/kultsi/kultsipuppeli (gold; darling (These are ordered from least syrupy to most syrupy.)
Mielitietty/mielitiettyni (favourite/my favourite (Formal, usually used when speaking about your loved one to someone else.))
Muru/murunen (crumb; honey)
Pikkuinen (little one (Used for children and animals.))
Rakas/rakkaani (love/my love; dear)
SydÀnkÀpyseni/sydÀnkÀpynen (my heart cone/heart cone; sweetheart)
Chéri (m) / Chérie (f) (darling)
Chou (used like "honey", but directly translates to cabbage)
L'/amour de ma vie (love of my life)
Liebling (beloved/favourite)
Schatz (treasure, I would say the most common one between established couples)
Liebes (loved one) (f, I don't find it that romantic)
Liebster (m) (loved one, bit old-fashioned)
Liebste (f) (loved one, bit old-fashioned)
Engel / Engelchen (angel)
Prinzessin (f) (princess)
Kleines (f) (little one, can be used in a cute way for women, but can also sound degrading or offensive)
ÎγΏÏη /ÎγΏÏη ÎŒÎżÏ
(love /my love) (the first can also be used among friends, usually between women, but both are very often used in romantic relationships)
ΚÏ
ÏÎź ÎŒÎżÏ
(my soul) (mostly romantic but can be used by a parent to their kid)
Chaim sheli ŚŚŚŚ Ś©ŚŚ (my life)
Neshama sheli Ś Ś©ŚŚ Ś©ŚŚ (my soul)
Lev sheli ŚŚ Ś©ŚŚ (my heart)
Ahoovi ŚŚŚŚŚ (m) (my love)
Ahoovati ŚŚŚŚŚȘŚ (f) (my love)
Meri jaan à€źà„à€°à„ à€à€Ÿà€š (f) (my life)
Mera jaan (m/n) (my life)
Rani à€°à€Ÿà€šà„ (f) (queen)
Sayang (to love/love, can be used as 'honey', doesn't have to be romantic)
Cintaku (my love, mostly used romantically)
Cucciola (puppy/cub) (mostly used for women, but you could say "cucciolo" for men)
Piccola (little one) (mostly for women, "piccolo" would be the male version)
Cara/caro (dear) (now mostly used by grandmas for grandkids but perfect for couples in the past or old couples nowadays
Patata/patatina (potato/little potato) (again mostly women when used romantically, "patato/patatino" for men, but they can also be used for pets, babies, your kids or anyone that you find cute)
Tata/tato (short version of papata/patato)
Polpetta/polpettina (meatball/little meatball) (very uncommon, but I've heard it used for girls)
Topolina (little mouse) (very uncommon, but could be used for girls)
Jagiya ìêž°ìŒÂ (honey/baby)
Aegiya ì êž°ìŒ (baby/little one)
Gongjunim êł”ìŁŒë (f) (princess)
Wangjanim ììë (m) (prince)
Nae Sarang ëŽ ìŹë (my love)
Gwiyomi ê·ì믞 (cutie)
Yeobo ìŹëłŽ (darling, loved one to a spouse)
Myszko (f) (little mouse for women romantic, or for young daughters)
Misiu (m) (diminutive bear, romantic for men)
Misiaczku (another form of the above but more intersex)
SĆoneczko (diminutive for sun, can be for children but also romantic for women)
PÄ
czusiu (diminutive doughnut, romantic partner)
BÄ
belku (bubble diminutive for young children, toddlers or infants)
Duszko moja (very outdated, meaning my soul, for women)
Serce moje (also old school, meaning my heart, unisex)
Gwiazdeczko (diminutive star, for girls and romantic female partner)
Kotek/Kotku (kitten, unisex)
MaĆa (literally: little (f), for women, can be romantic but also offensive if used by strangers)
Skarbie (my treasure, unisex)
Rybciu (diminutive for fish, little fish, for women)
ĆŒabko (diminutive for frog, little frog, for women)
Meu querido (m)/ minha querida (f) (my darling)
Meu docinho (my sweetheart)
Amado (m)/Amada (f) (my love)
Meu (m)/ minha (f) mais que tudo (my above overall) Meu tesouro (my treasure)
Meu bem/ meu benzinho (my goodness)
Meu doce/meu docinho (my sweet/ my little sweet)
Querido (m) / Querida (f) (darling)
Meu bem (untraslatable; something between "my dear" and "my treasure")
Meu docinho de coco (my coconut candy - really old slang, nowadays used only for fun)
Patroa (f) (it means a female boss; not ironic not aggressive, but used by men to describe their wives affectionately, eg. "I can't go today, my patroa is waiting for me at home")
Gato/gatinho (m) / gata/gatinha (f) (cat/little cat; if a person is pretty, they are called a "cat")
Lindinha (beautiful/cutie)
MozĂŁo or Mor (love, more like slang)
Iubi (Sweet heart/darling)
Draga mea (f) / Dragul meu (m) (my dear)
DulceaÈa mea (jam/honey)
lyubov' moya / Đ»ŃĐ±ĐŸĐČŃ ĐŒĐŸŃ (my love)
radost' moya / ŃĐ°ĐŽĐŸŃŃŃ ĐŒĐŸŃ (joy of mine)
dusha moya / ĐŽŃŃа ĐŒĐŸŃ (my soul)
schast'e moyo / ŃŃаŃŃŃĐ” ĐŒĐŸŃ (my happiness)
sokrovishche moyo / ŃĐŸĐșŃĐŸĐČĐžŃĐ” ĐŒĐŸŃ (my treasure)
solnyshko / ŃĐŸĐ»ĐœŃŃĐșĐŸ (sunny)
zolotce / Đ·ĐŸĐ»ĐŸŃŃĐ” (golden)
lyubimyj (m) + lyubimaya (f) / Đ»ŃĐ±ĐžĐŒŃĐč + Đ»ŃĐ±ĐžĐŒĐ°Ń (beloved)
dorogoj (m) + dorogaya (f) / ĐŽĐŸŃĐŸĐłĐŸĐč + ĐŽĐŸŃĐŸĐłĐ°Ń (darling, dear)
milyj (m) + milaya (f) / ĐŒĐžĐ»ŃĐč + ĐŒĐžĐ»Đ°Ń (dear but in more informal way)
kotik / ĐșĐŸŃĐžĐș (kitty) malysh / ĐŒĐ°Đ»ŃŃ (baby)
zajchik (m) + zajka (f) / заĐčŃĐžĐș + заĐčĐșа (bunny)
ptenchik / ĐżŃĐ”ĐœŃĐžĐș (little bird, hatchling)
rybka moya (f) / ŃŃбĐșа ĐŒĐŸŃ (my fish)
SreÄa(o) moja (my happiness)
MilĂĄÄik (bit cheesy, but means my lovely)
Kanmani [cun-mun-ee] (darling)
KocacıÄım/karıcıÄım
(my husband/my wife, but in a more endearing way, you can say it to a person you're not married yet but thinking about marrying)
Her Ćeyim (my everything)
YaĆama sebebim (my reason to live)
Ceylanım (My gazelle, it's a gorgeous creature like cmon)
GĂŒzel gözlĂŒm (My lover with beautiful eyes)
Nazlı yarim (My coy lover)
Kalbimin sahibi (the owner of my heart)
GĂŒzelim/yakıĆıklım (my beautiful/my handsome)
KediciÄim (my kitty/kitten)
BiriciÄim/bi'tanem (my one and only)
Balım (my honey) (can also say "bal dudaklım (my lover with honey lips)" if you feeling on fire)
Evimin direÄi (literally meaning "the post of my house," if you say this to a person (usually your husband), you mean to say that he keeps your household/family up, whether financially or with emotional maturity)
Đ·ŃŃĐŸĐœŃĐșа [zironÊčka] (star)
ĐŒŃĐč ŃĐČŃŃ [miy svit] (my world)
ĐŒĐŸŃ Đ¶ĐžŃŃŃ [moye zhyttya] (my life)
ĐŒĐŸŃ ŃĐ”ŃĐŽĐ”ĐœŃĐșĐŸ [moye serdenÊčko] (my heart)
ĐșĐŸŃ
Đ°ĐœĐžĐč [kokhanyy](m) /ĐșĐŸŃ
Đ°ĐœĐ° [kokhana] (f) (my beloved one)
ĐŒĐžĐ»ĐžĐč ĐŒŃĐč [mylyy miy] (m) / ĐŒĐžĐ»Đ° ĐŒĐŸŃ [myla moya] (f) (my dear one)
Đ»ŃбОĐč ĐŒŃĐč [lyubyy miy] (m) / Đ»Ńба ĐŒĐŸŃ [lyuba moya] (f) (my loved one)
ĐŒŃĐč ŃĐŽĐžĐœĐžĐč [miy yedynyy] (m) /ĐŒĐŸŃ ŃĐŽĐžĐœĐ° [moya yedyna] (f) (my only one)
ŃĐŸĐœŃĐ” [sontse], ŃĐŸĐœĐ”ŃĐșĐŸ [sonechko] (sun, sunshine)
ĐżŃаŃĐșа [ptashka] (f) (birdie)
ĐŽŃŃĐł (m)/ ĐżĐŸĐŽŃŃга (f) ĐŒĐŸŃŃ ĐŽŃŃŃ [druh (m)/podruha (f) moyeyi dushi] (a friend of my soul)
Meri jaan Ù
ÛŰ±Û ŰŹŰ§Ù (my life)
Pyaari ÙŸÛŰ§Ű±Û (sweetheart)
Shahzadi ŰŽÛŰČŰ§ŰŻÛ (f) (princess)
Let me know more terms of endearment in your languages! And please correct me if I'm wrong somewhere.
Please note that they are not all romantic. You can ask in the replies, so a native speaker can answer if it's appropiate for the type of relationship you want your characters to have.