I have read your comment about the "preedit" concept but it doesn't seem to work, at least on my system using xfce4.
Choosing input method zh-pinyin (m17n) and for example typing ai1, no underlined text appears. I tried zh-pinyin input in mousepad, gedit and kate editors, no preedit is shown and ctrl+alt+p doesn't open an input window. Trying input in xterm too doesn't open an input window. These are the packages I have installed: fcitx v.4.2.5 from Debian/experimental: fcitx-libs, fcitx-bin, fcitx-data, fcitx-config-common, fcitx-config-gtk, fcitx-frontend-gtk2, fcitx-frontend-gtk3, fcitx-modules (core modules), fcitx-module-dbus,fcitx-module-lua, fcitx-module-x11, fcitx-table, fcitx-tools, fcitx-ui-classic, fcitx-pinyin, fcitx-sunpinyin, fcitx-googlepinyin, fcitx-m17n. Could some package be missing? Using fcitx-pinyin, fcitx-sunpinyin or fcitx-googlepinyin woks, opening an input window but ctrl+alt+p doesn't show preedited text.
fcitx-config
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