Bertha sits next to 4 phonetic neighbors — Martha, Eartha, and Berta are the closest matches by sound. Most share Bertha's German-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"bright, shining"
"to circle, to spin"
"maiden, girl"
"rock, stone"
"strength of the spear"
"hazel meadow, clearing of hazel trees"
"white wave"
"gift of God"
"torch, radiance"
"thunder goddess, feminine Thor"
"rose flower, beauty"
"hill + meadow clearing"
"glowing white, pure, sincere"
"from the city of Rheims"
"town of the new law"
"dweller by the river"
"luminous, shining"
"land where rye is grown"
"pure, clean"
"black, dark-colored"
"pretty, cheerful"
Similar sound: These names share phonetic patterns with Bertha — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old High German 'beraht' origins, giving them the same cultural heritage as Bertha.
Rhythm: Bertha is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.