add i18n demo

examples/gui/i18n_demo/README.md

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+i18n demo
+=====
+
+Please **Open this forder** in MaixVision to run, the `locales` dir is important.
+
+## Usage
+
+1. Coding like `main.py`, use `tr` to translate strings.
+2. Execute command `maixtool i18n -d . -r` in this directory, this command will scan all source code and find all strings you want to translate and generate translation files in `locales` dir, like `en.yaml` or `zh.yaml`, the locale name can be found in [here](https://www.science.co.il/language/Locale-codes.php) or [wikipedia](https://en.wikipedia.org/wiki/Language_localisation), all letters use lower case.
+3. Translate yaml files mannually.
+4. Run this project.
+
+

examples/gui/i18n_demo/locales/en.yaml

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+hello: hello

examples/gui/i18n_demo/locales/zh.yaml

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+hello: 你好

examples/gui/i18n_demo/main.py

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+'''
+    Please read README.md of this dir fist!!!!!!!
+'''
+
+from maix import i18n, image, display, app, time, err
+
+trans = i18n.Trans()
+tr = trans.tr
+
+# load translations from translation files
+e = trans.load("locales")
+err.check_raise(e, "load translation yamls failed")
+
+# load Chinese font
+image.load_font("sourcehansans", "/maixapp/share/font/SourceHanSansCN-Regular.otf", size = 32)
+image.set_default_font("sourcehansans")
+
+disp = display.Display()
+
+img = image.Image(disp.width(), disp.height())
+
+# draw hello with system setting language
+print("system locale setting:", trans.get_locale())
+img.draw_string(2, 2, tr("hello"), image.Color.from_rgb(255, 0, 0))
+
+# manually set locale to zh
+trans.set_locale("zh")
+img.draw_string(2, 40, tr("hello"), image.Color.from_rgb(255, 0, 0))
+
+# manually set locale to en
+trans.set_locale("en")
+img.draw_string(2, 80, tr("hello"), image.Color.from_rgb(255, 0, 0))
+
+disp.show(img)
+while not app.need_exit():
+    time.sleep(1)
+