I wonder if I am the only one encountering that issue at the moment. The issue seemed to already have appeared in 2017 and got fixed: 

https://trailblazer.salesforce.com/issues_view?id=a1p3A000000jkxhQAA&title=values-saved-by-flow-using-picklist-choices-saving-translated-values-for-picklist-in-database

Here is an exact descrption of my issue (from my opened Case where Support told me to post it here):

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The Flow "[Opportunity] AddProductFlow" tries to save a translated value from a Picklist Choice set to a to be created Opportunity Record instead of the API value of that respective Picklist Choice, thus causing the Flow to fail as a wrong value is tried to be saved to a restricted picklist choice as a result of that.

Steps to reproduce (in our specific org):

• Log Into the Salesforce Org
• Go to the Translation Workbench
• Provide German translations for the Picklist Values used in a Picklist Choice set in a flow
• Switch user to the German Language
• Navigate to the respective flow
• Select a German Value from the translated Picklist Choices from the Picklist Choice set
• If the flow tries to save a record with the value from the Picklist Choice set, you should now receive a failed flow error

The error messsage from the flow is attached (Sorry for the German):

Fehlerelement CreateOpportunityProduct (FlowRecordCreate).
Dieser Fehler trat beim Erstellen von Datensätzen durch den Flow auf: INVALID_OR_NULL_FOR_RESTRICTED_PICKLIST: Calculation Mode: fehlerhafter Wert für eingeschränktes Auswahllistenfeld: Prozent. Sie können die ExceptionCode-Werte im SOAP API Developer Guide nachlesen.

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ZUWEISUNG: DefineOpportunityProductToCreate
{!OpportunityProductToCreate.Quantity} Gleich 1
{!OpportunityProductToCreate.Product2Id} Gleich {!GetPricebookEntryProduct.Id}
{!OpportunityProductToCreate.PricebookEntryId} Gleich {!GetPriceBookEntry.Id}
{!OpportunityProductToCreate.FeePercentage__c} Gleich {!FeePercentage}
{!OpportunityProductToCreate.ExpectedManagedValue__c} Gleich {!ExpectedManagedValue}
{!OpportunityProductToCreate.OpportunityId} Gleich {!GetCurrentOpportunity.Id}
{!OpportunityProductToCreate.Description} Gleich {!Description}
{!OpportunityProductToCreate.UnitPrice} Gleich {!Fee}
{!OpportunityProductToCreate.CalculationMode__c} Gleich {!CalculationModeFormula}
Ergebnis
{!OpportunityProductToCreate.Product2Id} = "01t5J000000R2BFQA0"
{!OpportunityProductToCreate.OpportunityId} = "0065J000002JajzQAC"
{!OpportunityProductToCreate.CalculationMode__c} = "Prozent" <<-------------------------- This is wrong. It should say "Percent" as "Percent" is the API Value of the Picklist Field. "Prozent" is only the German translation
{!OpportunityProductToCreate.PricebookEntryId} = "01u5J000000g2vWQAQ"
{!OpportunityProductToCreate.FeePercentage__c} = "0,4"
{!OpportunityProductToCreate.Quantity} = "1"
{!OpportunityProductToCreate.UnitPrice} = "null"
{!OpportunityProductToCreate.ExpectedManagedValue__c} = "8.000.000"
{!OpportunityProductToCreate.Description} = ""

SCHNELLERSTELLUNG: CreateOpportunityProduct
OpportunityLineItem-Datensätze mit den Werten erstellen, die in {!OpportunityProductToCreate} gespeichert sind.
Variablenwerte
[Quantity=1.0,Product2Id=01t5J000000R2BFQA0,PricebookEntryId=01u5J000000g2vWQAQ,FeePercentage__c=0.4,ExpectedManagedValue__c=8000000,OpportunityId=0065J000002JajzQAC,Description=,UnitPrice=null,CalculationMode__c=Prozent]
Ergebnis
Datensätze konnten nicht erstellt werden.