diff --git a/TalerCommon/Helper/CurrencySpecification.swift b/TalerCommon/Helper/CurrencySpecification.swift
index 5a6811ee..5ea2b6ac 100644
--- a/TalerCommon/Helper/CurrencySpecification.swift
+++ b/TalerCommon/Helper/CurrencySpecification.swift
@@ -181,29 +181,46 @@ public struct CurrencyInfo: Sendable {
         }
     }
 
+    /// Replace whichever currency markers the formatter actually has.
+    ///
+    /// `NumberFormatter.currencySymbol` and `.currencyCode` are
+    /// implicitly-unwrapped optionals, and both are nil when the formatter's
+    /// locale carries no region -- `de` rather than `de_DE`.  `CurrencyFormatter`
+    /// takes its locale from `Locale.autoupdatingCurrent`, so that happens
+    /// whenever the app runs with `-AppleLanguages`/`-AppleLocale` set to a bare
+    /// language, which is what Xcode's "Application Language" scheme option and
+    /// UI-test runs do.  Passing such a value straight to
+    /// `replacingOccurrences(of:)` traps and takes the app down.
+    private func replacingCurrencyMarkers(in aString: String,
+                                          with replacement: String) -> String {
+        var result = aString
+        if let symbol = formatter.currencySymbol, !symbol.isEmpty {
+            result = result.replacingOccurrences(of: symbol, with: replacement)
+        }
+        if let code = formatter.currencyCode, !code.isEmpty {
+            result = result.replacingOccurrences(of: code, with: replacement)
+        }
+        return result
+    }
+
     func currencyString(_ aString: String, useISO: Bool = false) -> String {
         if !useISO {
             if let aSymbol = altUnitSymbol {
-                let symbolString = aString.replacingOccurrences(of: formatter.currencySymbol, with: aSymbol)
-                return symbolString.replacingOccurrences(of: formatter.currencyCode, with: aSymbol)
+                return replacingCurrencyMarkers(in: aString, with: aSymbol)
             }
             if let aName = altUnitName0 {
                 let spacedName = formatter.leadingCurrencySymbol ? aName + SPACE
                                                                  : SPACE + aName
-                let spacedString1 = aString.replacingOccurrences(of: formatter.currencySymbol, with: spacedName)
-                let spacedString2 = spacedString1.replacingOccurrences(of: formatter.currencyCode, with: spacedName)
-                let spacedString3 = spacedString2.replacingOccurrences(of: "  ", with: " ")  // ensure we have only 1 space
-                return spacedString3
+                let spaced = replacingCurrencyMarkers(in: aString, with: spacedName)
+                return spaced.replacingOccurrences(of: "  ", with: " ")  // ensure we have only 1 space
             }
         }
         let currency = formatter.currency
         if !currency.isEmpty {
             let spacedName = formatter.leadingCurrencySymbol ? currency + SPACE
                                                              : SPACE + currency
-            let spacedString1 = aString.replacingOccurrences(of: formatter.currencySymbol, with: spacedName)
-            let spacedString2 = spacedString1.replacingOccurrences(of: formatter.currencyCode, with: spacedName)
-            let spacedString3 = spacedString2.replacingOccurrences(of: "  ", with: " ")  // ensure we have only 1 space
-            return spacedString3
+            let spaced = replacingCurrencyMarkers(in: aString, with: spacedName)
+            return spaced.replacingOccurrences(of: "  ", with: " ")  // ensure we have only 1 space
         }
         return aString
     }