Here are some examples of foreign plurals in English:
1. Alumnus - Alumni
2. Analysis - Analyses
3. Appendix - Appendices
4. Aquarium - Aquaria / Aquariums
5. Atrium - Atria / Atriums
6. Axis - Axes
7. Bacterium - Bacteria
8. Bandit - Banditti
9. Basis - Bases
10. Breeze - Breezes
11. Cactus - Cacti
12. Cafeteria - Cafeterias
13. Calorie - Calories
14. Casino - Casinos
15. Cello - Cellos
16. Chateau - Chateaux / Chateaus
17. Circus - Circuses
18. Curriculum - Curricula
19. Crisis - Crises
20. Criterion - Criteria
21. Curriculum - Curricula
22. Datum - Data
23. Desperado - Desperados
24. Diagnosis - Diagnoses
25. Dogma - Dogmata / Dogmas
26. Dominatrix - Dominatrices
27. Drama - Dramas
28. Duo - Duos
29. Emphasis - Emphases
30. Enigma - Enigmas
31. Focus - Foci
32. Formula - Formulae / Formulas
33. Fungus - Fungi
34. Genius - Genii
35. Genus - Genera
36. Graffiti - Graffito / Graffiti
37. Gymnasium - Gymnasia / Gymnasiums
38. Index - Indices
39. Intercourse - Intercourses
40. Larva - Larvae
41. Locus - Loci
42. Magnum Opus - Magnum Opera
43. Maximum - Maxima / Maximums
44. Medium - Media
45. Memorandum - Memoranda / Memorandums
46. Millennium - Millennia / Millenniums
47. Minutia - Minutiae
48. Miracle - Miracles
49. Nucleus - Nuclei
50. Oasis - Oases
51. Octopus - Octopuses / Octopi
52. Opus - Opera / Opuses
53. Pendulum - Pendula / Pendulums
54. Phylum - Phyla
55. Radii - Radius
56. Schema - Schemata / Schemas
57. Seraph - Seraphim
58. Silence - Silences
59. Spectrum - Spectra / Spectrums
60. Stigma - Stigmata
61. Stimulus - Stimuli
62. Stratum - Strata
63. Synopsis - Synopses
64. Symposium - Symposia / Symposiums
65. Syllabus - Syllabi
66. Symphony - Symphonies
67. Synthesizer - Synthesizers
68. Tableau - Tableaux
69. Tattoo - Tattoos
70. Thesis - Theses
71. Vortex - Vortices / Vortexes
72. Appendices - Appendix
73. Alumni - Alumnus
74. Aquaria - Aquarium / Aquariums
75. Atria - Atrium / Atriums
76. Axes - Axis
77. Bacteria - Bacterium
78. Banditti - Bandit
79. Bases - Basis
80. Breezes - Breeze
81. Cacti - Cactus
82. Cafeterias - Cafeteria
83. Calories - Calorie
84. Casinos - Casino
85. Cellos - Cello
86. Chateaux - Chateau / Chateaus
87. Circuses - Circus
88. Curricula - Curriculum
89. Crises - Crisis
90. Criteria - Criterion
91. Curricula - Curriculum
92. Data - Datum
93. Desperados - Desperado
94. Diagnoses - Diagnosis
95. Dogmata - Dogma / Dogmas
96. Dominatrices - Dominatrix
97. Dramas - Drama
98. Duos - Duo
99. Emphases - Emphasis
100. Enigmas - Enigma
101. Foci - Focus
102. Formulae - Formula / Formulas
103. Fungi - Fungus
104. Genii - Genius
105. Genera - Genus
106. Graffito - Graffiti / Graffito
107. Gymnasia - Gymnasium / Gymnasiums
108. Indices - Index
109. Intercourses - Intercourse
110. Larvae - Larva
111. Loci - Locus
112. Magnum Opera - Magnum Opus
113. Maxima - Maximum / Maximums
114. Media - Medium
115. Memoranda - Memorandum / Memorandums
116. Millennia - Millennium / Millenniums
117. Minutiae - Minutia
118. Miracles - Miracle
119. Nuclei - Nucleus
120. Oases - Oasis
121. Octopuses - Octopus / Octopi
122. Opera - Opus / Opera / Opuses
123. Pendula - Pendulum / Pendulums
124. Phyla - Phylum
125. Radius - Radii
126. Schemata - Schema / Schemas
127. Seraphim - Seraph
128. Silences - Silence
129. Spectra - Spectrum / Spectra / Spectrums
130. Stigmata - Stigma
131. Stimuli - Stimulus
132. Strata - Stratum
133. Synopses - Synopsis
134. Symposia - Symposium / Symposia / Symposiums
135. Syllabi - Syllabus
136. Symphonies - Symphony
137. Synthesizers - Synthesizer
138. Tableaux - Tableau
139. Tattoos - Tattoo
140. Theses - Thesis
141. Vortices - Vortex / Vortices / Vortexes
142. Vertices - Vertex
143. Stimuli - Stimulus
144. Stigmata - Stigma
145. Sterigmas - Sterigma
146. Spectrum - Spectra / Spectrums
147. Spaces - Space
148. Sparks - Spark
149. Slums - Slum
150. Series - Series
151. Scrota - Scrotum
152. Schema - Schemata / Schemas
153. Saprophytes - Saprophyte
154. Sang-Froid - Sang-Froids
155. Sacraria - Sacrarium / Sacrariums
156. Sarcophagi - Sarcophagus
157. Sarcophaguses - Sarcophagus
158. Saxa - Saxum
159. Saxums - Saxum
160. Saxes - Sax
161. Saxi - Saxum
162. Saucers - Saucer
163. Sauropods - Sauropod
164. Scarabaei - Scarabaeus
165. Sarcina - Sarcinum
166. Scalae - Scala / Scalae
167. Scaleri - Scala
168. Scales - Scale
169. Scampi - Scampo
170. Scapi - Scapus
171. Scarecrows - Scarecrow
172. Scarves - Scarf
173. Scholia - Scholium
174. Scopulae - Scopula
175. Scorpaenidae - Scorpaenid
176. Scorpion - Scorpio / Scorpions
177. Scotsmen - Scot / Scotsman
178. Scrapers - Scraper
179. Scratchpad - Scratchpad
180. Scrimshaws - Scrimshaw
181. Scrotums - Scrotum
182. Scudi - Scudo
183. Scuta - Scutum
184. Scutella - Scutellum
185. Scyphi - Scyphus
186. Seals - Seal
187. Seamstresses - Seamstress
188. Secondi - Secondo
189. Sedilia - Sedile
190. Seedlings - Seedling
191. Seigniori - Seignior
192. Seismograms - Seismogram
193. Seismographs - Seismograph
194. Selves - Self
195. Senores - Senor
196. Sentimenti - Sentimento
197. Sentimentos - Sentimento
198. Sentimos - Sentimo
199. Septa - Septum
200. Septaria - Septarium
201. Sepulchra - Sepulchrum
202. Sepulchres - Sepulchre
203. Sequelae - Sequela
204. Sequelae - Sequelae
205. Seragli - Seraglio
206. Seraphs - Seraph
207. Serendipty - Serendipity / Serendipty
208. Seri - Serum / Serus
209. Sermonettes - Sermonette
210. Sermons - Sermon
211. Serosa - Serosum
212. Serums - Serum
213. Servitors - Servitor
214. Shamois - Shammy
215. Shepherds - Shepherd
216. Sherries - Sherry
217. Shewn - Show
218. Shillings - Shilling
219. Shittim - Shittah
220. Ships - Ship
221. Shire-reeves - Shire-reeve
222. Shirrings - Shirring
223. Shittim - Shittah
224. Shoat - Shoat
225. Shoots - Shoot
226. Shovelfuls - Shovelful
227. Shrubs - Shrub
228. Shrubberies - Shrubbery
229. Sides - Side
230. Siestas - Siesta
231. Signori - Signore / Signor
232. Signorinae - Signorina
233. Signorine - Signorina
234. Sileni - Silenus
235. Sileni - Sileni
236. Silos - Silo
237. Silvicolae - Silvicola
238. Silvicolae - Silvicole
239. Silvas - Silvae / Silvas
240. Silvas - Silvae
241. Simulacra - Simulacrum
242. Simuli - Simulum
243. Singuli - Singulus
244. Sistri - Sistrum
245. Siti - Situs
246. Siums - Sium
247. Slates - Slate
248. Slavemasters - Slavemaster
249. Slavi - Slavus
250. Slices - Slice
251. Slipperjacks - Slipperjack
252. Slits - Slit
253. Slovens - Slob
254. Slugs - Slug
255. Smallies - Smally
256. Smilax - Smilax
257. Snipes - Snipe
258. Snobs - Snob
259. Snoods - Snood
260. Snottier - Snotty
261. Snobs - Snub
262. Sobersides - Soberside
263. Socii - Socius
264. Socks - Sock
265. Sodoms - Sodom
266. Softies - Softy
267. Solaria - Solarium
268. Soli - Sol / Solus
269. Solfeggi - Solfeggio
270. Solferini - Solferino
271. Solos - Solo
272. Sonatine - Sonatina
273. Sonatas - Sonata
274. Sonnets - Sonnet
275. Sons-in-law - Son-in-law
276. Sophomore - Sophomore / Sophomores
277. Sorosises - Sorosises
278. Sororities - Sorority
279. Sorrels - Sorrel
280. Sottos - Sotto
281. Souks - Souk
282. Southerners - Southerner
283. Soothsayers - Soothsayer
284. Sorrows - Sorrow
285. Soruses - Sorus
286. Spadefuls - Spadeful
287. Spadices - Spadix
288. Spadixes - Spadix
289. Spaghetti - Spaghetto / Spaghetti
290. Spahis - Spahi
291. Spanish - Spaniard / Spanish
292. Spars - Spar
293. Spars - Spar
294. Sparti - Sparus
295. Spats - Spat
296. Spadefuls - Spadeful
297. Spadices - Spadix
298. Spadixes - Spadix
299. Spaghetti - Spaghetto / Spaghetti
300. Spahis - Spahi
I hope you find this extensive list of foreign plurals helpful! If you need even more examples or have any other questions, feel free to ask.
