diff --git a/apps/client/src/app/directives/localized-number/localized-number.directive.spec.ts b/apps/client/src/app/directives/localized-number/localized-number.directive.spec.ts
new file mode 100644
index 000000000..181398e9e
--- /dev/null
+++ b/apps/client/src/app/directives/localized-number/localized-number.directive.spec.ts
@@ -0,0 +1,112 @@
+import { Component } from '@angular/core';
+import { ComponentFixture, TestBed } from '@angular/core/testing';
+import { FormControl, ReactiveFormsModule } from '@angular/forms';
+
+import { GfLocalizedNumberDirective } from './localized-number.directive';
+
+@Component({
+  imports: [GfLocalizedNumberDirective, ReactiveFormsModule],
+  template: `
+    <input gfLocalizedNumber [formControl]="control" [locale]="locale" />
+  `
+})
+class TestHostComponent {
+  public control = new FormControl<number | null>(null);
+  public locale = 'en-US';
+}
+
+describe('GfLocalizedNumberDirective', () => {
+  let fixture: ComponentFixture<TestHostComponent>;
+  let host: TestHostComponent;
+  let input: HTMLInputElement;
+
+  beforeEach(async () => {
+    await TestBed.configureTestingModule({
+      imports: [TestHostComponent]
+    }).compileComponents();
+
+    fixture = TestBed.createComponent(TestHostComponent);
+    host = fixture.componentInstance;
+    fixture.detectChanges();
+    input = fixture.nativeElement.querySelector('input');
+  });
+
+  function typeValue(value: string) {
+    input.value = value;
+    input.dispatchEvent(new Event('input'));
+    fixture.detectChanges();
+  }
+
+  it('should force type="text" and inputmode="decimal"', () => {
+    expect(input.getAttribute('type')).toBe('text');
+    expect(input.getAttribute('inputmode')).toBe('decimal');
+  });
+
+  it('should parse English grouped numbers', () => {
+    host.locale = 'en-US';
+    fixture.detectChanges();
+
+    typeValue('1,234.50');
+    expect(host.control.value).toBe(1234.5);
+
+    typeValue('1234.50');
+    expect(host.control.value).toBe(1234.5);
+  });
+
+  it('should parse German grouped numbers', () => {
+    host.locale = 'de-DE';
+    fixture.detectChanges();
+
+    typeValue('1.234,50');
+    expect(host.control.value).toBe(1234.5);
+
+    typeValue('1234,50');
+    expect(host.control.value).toBe(1234.5);
+
+    typeValue('12.345.678,90');
+    expect(host.control.value).toBe(12345678.9);
+  });
+
+  it('should set null for empty or invalid input', () => {
+    typeValue('');
+    expect(host.control.value).toBeNull();
+
+    typeValue('   ');
+    expect(host.control.value).toBeNull();
+
+    typeValue('abc');
+    expect(host.control.value).toBeNull();
+  });
+
+  it('should write programmatic values to the input', () => {
+    host.control.setValue(1234.5);
+    fixture.detectChanges();
+
+    expect(input.value).toBe('1234.5');
+
+    host.control.setValue(null);
+    fixture.detectChanges();
+
+    expect(input.value).toBe('');
+  });
+
+  it('should keep required validation working', () => {
+    host.locale = 'de-DE';
+    host.control.setValidators([
+      (control) => {
+        return control.value === null || control.value === undefined
+          ? { required: true }
+          : null;
+      }
+    ]);
+    host.control.updateValueAndValidity();
+    fixture.detectChanges();
+
+    typeValue('');
+    expect(host.control.hasError('required')).toBe(true);
+
+    typeValue('1.234,50');
+    expect(host.control.hasError('required')).toBe(false);
+    expect(host.control.value).toBe(1234.5);
+  });
+});
diff --git a/apps/client/src/app/directives/localized-number/localized-number.directive.ts b/apps/client/src/app/directives/localized-number/localized-number.directive.ts
new file mode 100644
index 000000000..cf8a80507
--- /dev/null
+++ b/apps/client/src/app/directives/localized-number/localized-number.directive.ts
@@ -0,0 +1,87 @@
+import { DEFAULT_LOCALE } from '@ghostfolio/common/config';
+import { extractNumberFromString } from '@ghostfolio/common/helper';
+
+import { DOCUMENT } from '@angular/common';
+import { Directive, ElementRef, inject, input } from '@angular/core';
+import { ControlValueAccessor, NgControl } from '@angular/forms';
+
+@Directive({
+  host: {
+    '(blur)': 'handleBlur()',
+    '(input)': 'handleInput()',
+    '[attr.inputmode]': '"decimal"',
+    '[attr.type]': '"text"'
+  },
+  selector: 'input[gfLocalizedNumber]'
+})
+export class GfLocalizedNumberDirective implements ControlValueAccessor {
+  public readonly locale = input<string>();
+
+  private readonly document = inject(DOCUMENT);
+  private readonly elementRef =
+    inject<ElementRef<HTMLInputElement>>(ElementRef);
+
+  public constructor() {
+    const ngControl = inject(NgControl, { optional: true, self: true });
+
+    if (ngControl) {
+      // Replace DefaultValueAccessor so the FormControl stores a number
+      ngControl.valueAccessor = this;
+    }
+  }
+
+  public handleBlur() {
+    this.onTouched();
+  }
+
+  public handleInput() {
+    const value = this.elementRef.nativeElement.value;
+
+    if (!value?.trim()) {
+      this.onChange(null);
+      return;
+    }
+
+    // Locale resolution priority:
+    //   1. explicit [locale] input from the template
+    //   2. document.documentElement.lang — set by Angular i18n to the active
+    //      language (e.g. 'de' when the app runs under /de/)
+    //   3. DEFAULT_LOCALE ('en-US') as the final fallback
+    const localeInput = this.locale();
+    const documentLang = this.document.documentElement.lang;
+    const resolvedLocale = localeInput ?? documentLang ?? DEFAULT_LOCALE;
+
+    const parsedNumber = extractNumberFromString({
+      locale: resolvedLocale,
+      value
+    });
+
+    this.onChange(
+      parsedNumber !== undefined && !Number.isNaN(parsedNumber)
+        ? parsedNumber
+        : null
+    );
+  }
+
+  public registerOnChange(fn: (value: number | null) => void) {
+    this.onChange = fn;
+  }
+
+  public registerOnTouched(fn: () => void) {
+    this.onTouched = fn;
+  }
+
+  public setDisabledState(isDisabled: boolean) {
+    this.elementRef.nativeElement.disabled = isDisabled;
+  }
+
+  public writeValue(value: number | null) {
+    this.elementRef.nativeElement.value =
+      value === null || value === undefined || Number.isNaN(value)
+        ? ''
+        : String(value);
+  }
+
+  private onChange: (value: number | null) => void = () => undefined;
+  private onTouched: () => void = () => undefined;
+}
diff --git a/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.component.ts b/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.component.ts
index 632db1cd4..bfb87177d 100644
--- a/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.component.ts
+++ b/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.component.ts
@@ -1,3 +1,4 @@
+import { GfLocalizedNumberDirective } from '@ghostfolio/client/directives/localized-number/localized-number.directive';
 import { UserService } from '@ghostfolio/client/services/user/user.service';
 import { ASSET_CLASS_MAPPING, DEFAULT_LOCALE } from '@ghostfolio/common/config';
 import { CreateOrderDto, UpdateOrderDto } from '@ghostfolio/common/dtos';
@@ -57,6 +58,7 @@ import { ActivityType } from './types/activity-type.type';
   host: { class: 'h-100' },
   imports: [
     GfEntityLogoComponent,
+    GfLocalizedNumberDirective,
     GfSymbolAutocompleteComponent,
     GfTagsSelectorComponent,
     GfValueComponent,
@@ -124,7 +126,8 @@ export class GfCreateOrUpdateActivityDialogComponent {
       this.data.user?.permissions,
       permissions.createOwnTag
     );
-    this.locale = this.data.user.settings.locale ?? DEFAULT_LOCALE;
+    this.locale =
+      this.data.user.settings.locale ?? this.locale ?? DEFAULT_LOCALE;
     this.mode = this.data.activity?.id ? 'update' : 'create';
 
     this.dateAdapter.setLocale(this.locale);
diff --git a/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.html b/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.html
index b5dbf4669..81855a1e7 100644
--- a/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.html
+++ b/apps/client/src/app/pages/portfolio/activities/create-or-update-activity-dialog/create-or-update-activity-dialog.html
@@ -181,7 +181,7 @@
     >
       <mat-form-field appearance="outline" class="w-100">
         <mat-label i18n>Quantity</mat-label>
-        <input formControlName="quantity" matInput type="number" />
+        <input formControlName="quantity" gfLocalizedNumber matInput />
       </mat-form-field>
     </div>
     <div
@@ -209,7 +209,7 @@
               }
             }
           </mat-label>
-          <input formControlName="unitPrice" matInput type="number" />
+          <input formControlName="unitPrice" gfLocalizedNumber matInput />
           <div
             class="ml-2"
             matTextSuffix
@@ -254,7 +254,7 @@
     >
       <mat-form-field appearance="outline" class="w-100">
         <mat-label i18n>Fee</mat-label>
-        <input formControlName="fee" matInput type="number" />
+        <input formControlName="fee" gfLocalizedNumber matInput />
         <div
           class="ml-2"
           matTextSuffix
diff --git a/libs/common/src/lib/helper.spec.ts b/libs/common/src/lib/helper.spec.ts
index d33f10452..d06142c8e 100644
--- a/libs/common/src/lib/helper.spec.ts
+++ b/libs/common/src/lib/helper.spec.ts
@@ -53,6 +53,27 @@ describe('Helper', () => {
       ).toEqual(-99999.99);
     });
 
+    it('Get decimal number with thousands separator (de-DE)', () => {
+      expect(
+        extractNumberFromString({ locale: 'de-DE', value: '1.234,50' })
+      ).toEqual(1234.5);
+      expect(
+        extractNumberFromString({ locale: 'de-DE', value: '1234,50' })
+      ).toEqual(1234.5);
+      expect(
+        extractNumberFromString({ locale: 'de-DE', value: '12.345.678,90' })
+      ).toEqual(12345678.9);
+    });
+
+    it('Get decimal number with thousands separator (en-US)', () => {
+      expect(
+        extractNumberFromString({ locale: 'en-US', value: '1,234.50' })
+      ).toEqual(1234.5);
+      expect(
+        extractNumberFromString({ locale: 'en-US', value: '1234.50' })
+      ).toEqual(1234.5);
+    });
+
     it('Get decimal number (comma notation) for locale where currency is not grouped by default', () => {
       expect(
         extractNumberFromString({ locale: 'es-ES', value: '999,99' })