I found this https://trailhead.salesforce.com/trailblazer-community/feed/0D54V00007ReVvRSAV - seems like you should use Resource Formula: Here's how to use Resource Formula to add custom labels to FSL mobile flows:
Create a custom label definition in your Salesforce org. Create a Resource Formula record in your Salesforce org. The formula should return the value of the custom label. In your FSL mobile flow, reference the Resource Formula record in the Value property of the screen or component that needs the label. Here's an example of how to use Resource Formula to add a custom label to a text component:
Create a custom label definition with the following details: Label Name: My_Custom_Label Label Value: This is my custom label Create a Resource Formula record with the following details: Formula: {!GET('My_Custom_Label')} In your FSL mobile flow, add a text component and set the Value property to the Resource Formula record you created. The text component will now display the value of the My_Custom_Label custom label. Here's an example of how to use Resource Formula to add a translation to a button component:
Create a custom label definition with the following details: Label Name: Button_Label_English Label Value: English button label Create another custom label definition with the following details: Label Name: Button_Label_Spanish Label Value: Spanish button label Create a Resource Formula record with the following details: Formula: $Language == 'en_US' ? {!GET('Button_Label_English')} : {!GET('Button_Label_Spanish')} In your FSL mobile flow, add a button component and set the Label property to the Resource Formula record you created. The button component will now display the appropriate label based on the user's locale.